An Open Mind; Mindmelds and Empaths
Self-published: ICON 1 (2007 PDF)

An Opportunity for Profit
TSR: Fiction (1998 )

O, Wintry Song of Agony
EN Publishing: d20 3.5 (2007 )
EN Publishing: Dungeons & Dragons 4 (2010 PDF)

O.S.R.I.C.
Usherwood Publishing: OSRIC 2.2 (2011 Digest)

O.S.R.I.C. Book for Assassins
World Gorean Society: OSRIC 2 (2010 PDF)

O.S.R.I.C. Second Edition
Black Blade Publishing: OSRIC 2.2 (2011 Hardcover)
Usherwood Publishing: OSRIC 2.2 (2011 Hardcover)
Black Blade Publishing: OSRIC 2.2 (2012 Hardcover)
Usherwood Publishing: OSRIC 2.2 (2012 Hardcover)

O1: Harbinger of Darkness
Underworld Publishing: AD&D 2 (1992 )

O1: The Gem and the Staff
TSR: D&D / Basic 2 (1983 )

O2: Blade of Vengeance
TSR: D&D / Basic 2 (1983 )

OA1: Swords of the Daimyo
TSR: AD&D 1 (1986 )

OA2: Night of the Seven Swords
TSR: AD&D 1 (1986 )

OA3: Ochimo: The Spirit Warrior
TSR: AD&D 1 (1987 )

OA4: Blood of the Yakuza
TSR: AD&D 1 (1987 )

OA5: Mad Monkey vs the Dragon Claw
TSR: AD&D 1 (1989 )

OA6: Ronin Challenge
TSR: AD&D 2 (1990 )

OA7: Test of the Samurai
TSR: AD&D 2 (1990 )

Oak, Ash, & Thorn: The Changeling: The Lost Second Edition Companion
Onyx Path Publishing: Changeling: The Lost 2 (2020 )

Oakling Player Character Race
Alluria Publishing: Dungeons & Dragons 4 (2008 PDF)
Alluria Publishing: Pathfinder 1 (2009 PDF)

Oasis
Dark City Games: Legends of Time and Space 1 (2007 )

Oath of Nerull
Wizards of the Coast: Fiction (2002 )

Oath of Vigilance
Wizards of the Coast: Fiction (2011 )

Oathbound Seven
Epidemic Books: Pathfinder 1 (2011 Hardcover)
Epidemic Books: Pathfinder 1 (2011 Hardcover)

Oathbound: Arena
Bastion Press: d20 3 (2003 )

Oathbound: Domains of the Forge
Bastion Press: d20 3 (2002 Hardcover)

Oathbound: Eclipse
Epidemic Books: d20 3.5 (2010 )

Oathbound: Mysteries of Arena
Bastion Press: d20 3.5 (2004 )

Oathbound: Plains of Penance
Bastion Press: d20 3 (2002 )

Oathbound: Wrack & Ruin
Bastion Press: d20 3 (2003 )

Oaths of the Riddermark
Cubicle 7 Entertainment: One Ring 1 (2017 Hardcover)

Obia
Dark Phoenix Publishing: L.I.F.E. System 2 (2014 PDF)

Obitu Player Character Race
Alluria Publishing: Dungeons & Dragons 4 (2008 PDF)
Alluria Publishing: Pathfinder 1 (2009 PDF)

Objective Interim Modern Combat System
SPQR Studios: Generic / One-Off System 1 (2005 PDF)

Objective Zebra
Bully Pulpit Games: Fiasco 1 (2011 PDF)

Objects Below the Shattered Moon: Volume 1
Expeditious Retreat Press: Sorcery & Super Science! 1 (2010 PDF)

Objects Below the Shattered Moon: Volume 2
Expeditious Retreat Press: Sorcery & Super Science! 1 (2010 PDF)

Objects Below the Shattered Moon: Volume 3
Expeditious Retreat Press: Sorcery & Super Science! 1 (2011 PDF)

Oblivion
White Wolf Publishing: Mind's Eye Theatre 2 (1997 )

Oblivion's Edge
Deathwatch: Deathwatch 1 (2010 PDF)

Obregon's Dishonor
Brave Halfling Publishing: D&D / Original 1 (2009 PDF)

Obscene Serpent Religion
Neoplastic Press: Lamentations of the Flame Princess 3 (2014 )

Observer Effect
Arc Dream Publishing: Delta Green 1 (2016 )

Obsidian LARP Quickstart
Twilight Games: Generic / One-Off System 1 (2005 )

The Obsidian Oracle
TSR: Fiction (1993 )
Wizards of the Coast: Fiction (2009 TPB)

Obsidian Ridge
Wizards of the Coast: Fiction (2008 )

Obsidian Twilight Campaign Setting
LPJ Design: Pathfinder 1 (2010 PDF)

Obsidian: The Age of Judgement
Apophis Consortium: Obsidian (1999 )
Apophis Consortium: Obsidian 2 (2001 Hardcover)

Occult Adventures
Paizo Publishing: Pathfinder 1 (2015 Hardcover)

Occult Items of Power
Fast Forward Entertainment: d20 3 (2002 Hardcover)

Occult Lore
Atlas Games: d20 3 (2002 Hardcover)

Occult Mysteries
Paizo Publishing: Pathfinder 1 (2014 )

The Octagon of Chaos
Theatre of the Mind Enterprises: Stormbringer 2 (1986 )

octaNe
Memento Mori Theatricks: octaNe (2002 )

October Rust
Common Fortress: October Rust 1 (2021 PDF)

October's Shadows
Self-published: October's Shadows 1 (2005 PDF)

Octopussy
Victory Games: James Bond 007 1 (1983 )

OD&DITIES #1
Self-published: D&D / Basic (2000 PDF)

OD&DITIES #2
Self-published: D&D / Basic (2000 PDF)

OD&DITIES #3
Self-published: D&D / Basic (2001 PDF)

OD&DITIES #4
Self-published: D&D / Basic (2001 PDF)

OD&DITIES #5
Self-published: D&D / Basic (2001 PDF)

OD&DITIES #6
Self-published: D&D / Basic (2001 PDF)

OD&DITIES #7
Self-published: D&D / Basic (2002 PDF)

OD&DITIES #8
Self-published: D&D / Basic (2002 PDF)

OD&DITIES #9
Self-published: D&D / Basic (2003 PDF)

OD&DITIES #10
Transfinite Publications: D&D / Basic (2003 PDF)

OD&DITIES #11
Self-published: D&D / Basic (2003 PDF)

OD&DITIES #12
Self-published: D&D / Basic (2004 PDF)

OD&DITIES #13
Self-published: Labyrinth Lord 2 (2010 PDF)

OD&DITIES #14
Self-published: Labyrinth Lord 2 (2010 PDF)

OD&DITIES #15
Self-published: Labyrinth Lord 2 (2010 PDF)

Odd Jobs
Mongoose Publishing: Spycraft 2 (2009 )
Crafty Games: Spycraft 2 (2009 )

Odditional Materials
Lost Pages: Into the Odd 1 (2015 )

ODDS #1
Farsight Games, UK: Generic 1 (2008 )

ODDS #2
Farsight Games, UK: Generic 1 (2008 )

ODDS #3: Sci-Fi Special
Farsight Games, UK: Generic 1 (2008 )

ODDS #4
Farsight Games, UK: Generic 1 (2009 )

ODDS #5
Farsight Games, UK: Generic 1 (2009 )

ODDS #6
Farsight Games, UK: Generic 1 (2009 )

ODDS #7
Farsight Games, UK: Generic 1 (2009 )

ODDS #8
Farsight Games, UK: Generic 1 (2009 )

ODDS #9: Last Issue!
Farsight Games, UK: Generic 1 (2009 )

Odessa Cache
Brutal Games: Decima System 1 (2008 PDF)

Odysseus
Fantasy Games Unlimited: Odysseus 1 (1980 )

Odyssey
Wizards of the Coast: Fiction (2001 )

Odyssey of the Dragonlords
Modiphius Entertainment: Dungeons & Dragons 5 (2019 Hardcover)
Arcanum Worlds: Dungeons & Dragons 5 (2019 Hardcover)

Odyssey Prime
Misfit Studios: d20 Modern 1 (2006 PDF)
Eden Studios: d20 Modern 1 (2006 PDF)
Misfit Studios: Unisystem 2 (2006 PDF)
Eden Studios: Unisystem 2 (2006 PDF)
Misfit Studios: d20 Modern 1 (2010 Hardcover)
Eden Studios: d20 Modern 1 (2010 Hardcover)
Misfit Studios: Unisystem 2 (2010 Hardcover)
Eden Studios: Unisystem 2 (2010 Hardcover)
Misfit Studios: d20 Modern 1 (2010 )
Eden Studios: d20 Modern 1 (2010 )
Misfit Studios: Unisystem 2 (2010 )
Eden Studios: Unisystem 2 (2010 )

Odyssey Prime: Southern Discomfort
Misfit Studios: d20 Modern 1 (2006 PDF)
Misfit Studios: Unisystem 2 (2006 PDF)
Misfit Studios: d20 Modern 1 (2010 )
Eden Studios: d20 Modern 1 (2010 )
Misfit Studios: Unisystem 2 (2010 )
Eden Studios: Unisystem 2 (2010 )

The Oerth Journal #1
The Oerth Journal: AD&D 2 (1995 PDF)

The Oerth Journal #2
Council of Greyhawk: Generic 1 (1995 PDF)

The Oerth Journal #3
Council of Greyhawk: AD&D 2 (1996 PDF)

The Oerth Journal #4
Council of Greyhawk: AD&D 2 (1996 PDF)

The Oerth Journal #5
Council of Greyhawk: AD&D 2 (1997 PDF)

The Oerth Journal #6
Council of Greyhawk: AD&D 2 (1997 PDF)

The Oerth Journal #7
Council of Greyhawk: AD&D 2 (1998 PDF)

The Oerth Journal #8
Council of Greyhawk: AD&D 2 (1998 PDF)

The Oerth Journal #9
Council of Greyhawk: AD&D 2 (1999 PDF)

The Oerth Journal #10: Discovery & Exploration
Council of Greyhawk: AD&D 2 (1999 PDF)

The Oerth Journal #11
Council of Greyhawk: AD&D 2 (2000 PDF)

The Oerth Journal #12: Recompilation
Council of Greyhawk: AD&D 2 (2002 PDF)

The Oerth Journal #13: Recompilation
Council of Greyhawk: Generic 1 (2002 PDF)

The Oerth Journal #14: Recompilation
Council of Greyhawk: Generic 1 (2002 PDF)

The Oerth Journal #15
Council of Greyhawk: Generic 1 (2004 PDF)

The Oerth Journal #16: A Chronicle of the Lands and People of the Flanaess
Council of Greyhawk: Generic 1 (2005 PDF)

The Oerth Journal #17
Council of Greyhawk: Generic 1 (2005 PDF)

The Oerth Journal #18: Electrum Anniversary Edition
Council of Greyhawk: Generic 1 (2006 PDF)

The Oerth Journal #19
Council of Greyhawk: Generic 1 (2006 PDF)

The Oerth Journal #20
Council of Greyhawk: Generic 1 (2006 PDF)

The Oerth Journal #21
Council of Greyhawk: Dungeons & Dragons 3.5 (2007 PDF)

The Oerth Journal #22
Council of Greyhawk: Dungeons & Dragons 3.5 (2007 PDF)

The Oerth Journal #23: Maure Castle Special Edition
Council of Greyhawk: Dungeons & Dragons 3.5 (2008 PDF)

The Oerth Journal #24
Self-published: Dungeons & Dragons 3.5 (2008 PDF)

The Oerth Journal #25: 25th Anniversary Gary Gygax Tribute Issue
Self-published: Dungeons & Dragons 3.5 (2009 PDF)

Of Aged Angels
Wizards of the Coast: Fiction (2001 )

Of Beasts and Men
Driftwood Publishing: The Riddle of Steel 1 (2003 )

Of Dust-Spice and Dewclaws
Mongoose Publishing: Traveller / Mongoose 1 (2010 PDF)

Of Gods & Heroes
Green Fairy Games: Generic / One-Off System 1 (2014 )

Of Gods & Monsters
Troll Lord Games: Castles & Crusades 1 (2009 )
Troll Lord Games: Castles & Crusades 1 (2010 Hardcover)
Troll Lord Games: Castles & Crusades 1 (2010 Digest)
Troll Lord Games: Castles & Crusades 1 (2009 )

Of Gods and Men
Non Sequitur Productions: Generic / One-Off System 1 (1991 )

Of Gods and Men
Triple Ace Games: Savage Worlds 2 (2010 PDF)

Of Places Most Foul
Mystic Eye Games: d20 3 (2001 )

Of Shadows Yet to Come
White Wolf Publishing: Storytelling System: Scion 1 (2007 )

Of Ships and the Sea
TSR: AD&D 2 (1997 )

Of Skulls and Scrapfaggot Green
Judges Guild: D&D / Original 1 (1979 )

Of Sound Mind
Sword & Sorcery: d20 3 (2002 )
Fiery Dragon: d20 3 (2002 )

The Official Advanced Dungeons & Dragons Coloring Album
Troubador Press: Generic 1 (1979 )

The Official Price Guide to Role-Playing Games
House of Collectibles: Generic 1 (1998 )

The Official Superhero Adventure Game
Self-published: Generic 1 (1981 )

Og
Wingnut Games: Og 1 (1995 )
Firefly Games: Og 3 (2007 )

OGL Ancients
Mongoose Publishing: OGL Ancients 1 (2004 Hardcover)

OGL Barbarian: Barbaric Treasures
Misfit Studios: d20 3.5 (2005 PDF)

OGL Barbarian: The Barbaric Sorcerer
Misfit Studios: d20 3.5 (2005 PDF)

OGL Barbarian: The Barbaric Warrior
Misfit Studios: d20 3.5 (2005 )

OGL Barbarian: The Child of Set
Misfit Studios: d20 3.5 (2005 PDF)

OGL Barbarian: The Deep Wilder
Misfit Studios: d20 3.5 (2005 PDF)

OGL Barbarian: The Hawkeye
Misfit Studios: d20 3.5 (2005 PDF)

OGL Barbarian: The Sea Devil
Misfit Studios: d20 3.5 (2005 PDF)

OGL Cybernet
Mongoose Publishing: OGL Cybernet 1 (2003 Hardcover)

OGL Horror
Mongoose Publishing: OGL Horror 1 (2003 Hardcover)

OGL Steampunk
Mongoose Publishing: OGL Steampunk 1 (2004 Hardcover)

OGL Wild West
Mongoose Publishing: OGL Wild West 1 (2004 Hardcover)

OGL-Fantasy Lite: Basic Player's Guide
S.T. Cooley Publishing: d20 3.5 (2004 PDF)

Ogre / G.E.V
Steve Jackson Games: Ogre 5 (2000 Box)

Ogre Battlefields
Steve Jackson Games: Ogre 5 (2001 Box)

The Ogre Book
Steve Jackson Games: Ogre 5 (2000 )

The Ogre City of Drahk'Suhl
AEG: d20 3 (2002 )

Ogre Hunt
Tentacles Press: Fiction (2017 )

Ogre Miniatures
Steve Jackson Games: Ogre Miniatures 1 (1992 )

Ogre Smash!
Destination Games: Generic 1 (1996 Digest)

Ohunkakan: The Living Myths
Monte Cook Games: The Strange 1 (2015 PDF)

Oil Pressure
Monkey House Games: Villains and Vigilantes 2.1 (2010 PDF)
Monkey House Games: Living Legends 1 (2010 PDF)

The Old Absinthe House Blues
Pinnacle: Savage Worlds 2 (2013 PDF)

Old Dragon
Redbox Editora: Old Dragon 1 (2011 )

The Old God's Return
Goodman Games: Dungeon Crawl Classics 1 (2013 )

Old Gods: A Campaign Frame for Mortal Coil
Galileo Games: Mortal Coil 2 (2010 PDF)

Old Hrolmar
Chaosium: Elric! 1 (2006 )

Old Lighthouse
0one Games: Generic 1 (2006 PDF)

The Old Man of Damascus
Skirmisher Publishing: Cthulhu Live 3 (2007 PDF)

The Old Powers
Ragnarok Enterprises: Ysgarth 4 (1984 Digest)

The Old Rock Tower
Unicorn Rampant Publishing: d20 3.5 (2008 PDF)
Unicorn Rampant Publishing: Dungeons & Dragons 4 (2009 PDF)

Old School Hack
Self-published: Old School Hack 1 (2010 PDF)
Self-published: Old School Hack (2011 PDF)

Old School Monster Classes
Quasar Knight Enterprises: Labyrinth Lord 2 (2014 PDF)

Old Soldiers Never Die
FASA Corporation: Star Trek 2 (1986 )

The Old Stone Fort
Steve Jackson Games: GURPS 3 (1988 )

Old Vinnengael: City of Sorrows
Corsair Publishing: Sovereign Stone 1 (2000 )
Sovereign Press: d20 3 (2002 )

Old World Armoury
Black Industries, UK: Warhammer Fantasy Roleplay 2 (2005 Hardcover)

Old World Bestiary
Black Industries, UK: Warhammer Fantasy Roleplay 2 (2005 Hardcover)

Old-School Essentials Advanced Fantasy Player's Tome
Necrotic Gnome: Old-School Essentials 2 (2021 )

Old-School Essentials Advanced Fantasy Referee's Tome
Necrotic Gnome: Old-School Essentials 2 (2021 )

Old-School Essentials Advanced Fantasy Reference Booklet
Necrotic Gnome: Old-School Essentials 2 (2021 PDF)

Old-School Essentials Advanced Fantasy: Druid and Illusionist Spells
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Advanced Fantasy: Genre Rules
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Advanced Fantasy: Monsters
Necrotic Gnome: Old-School Essentials 2 (2021 )

Old-School Essentials Advanced Fantasy: Treasures
Necrotic Gnome: Old-School Essentials 2 (2021 )

Old-School Essentials Black Box
Necrotic Gnome: Old-School Essentials 1 (2019 Box)

Old-School Essentials Classic Fantasy Referee's Screen
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Classic Fantasy: Basic Rules
Necrotic Gnome: Old-School Essentials 2 (2019 PDF)

Old-School Essentials Classic Fantasy: Cleric and Magic-User Spells
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Classic Fantasy: Genre Rules
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Classic Fantasy: Monsters
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials Classic Fantasy: Player's Rules Tome
Necrotic Gnome: Old-School Essentials 2 (2020 )

Old-School Essentials Classic Fantasy: Rules Tome
Necrotic Gnome: Old-School Essentials 1 (2019 )

Old-School Essentials Classic Fantasy: Treasures
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Essentials: Core Rules
Necrotic Gnome: Old-School Essentials 2 (2019 )

Old-School Magic
Vigilance Press: OSRIC 1 (2010 PDF)

Old-School Psionics
Vigilance Press: OSRIC 2 (2010 PDF)

Olde School Monk
Mob United Media: OSRIC 1 (2006 PDF)

Olde School Swashbuckler
Mob United Media: OSRIC 1 (2006 PDF)

Olenar's Heartstone
Fantasy Flight Games: d20 3 (2001 )

Olokand Castle
Columbia Games: Generic (2003 Looseleaf)

Olympian Breed
Palewolf Publishing: Savage Worlds (2012 PDF)

Olympian Breed Act One: A Gathering of Heroes
Palewolf Publishing: Savage Worlds 1 (2012 PDF)

The Olympians
Hero Games: HERO 4 (1990 )
I.C.E.: HERO 4 (1990 )

Omegakron
Avalon Hill: Lords of Creation 1 (1984 Box)

OmegaZone Instant Setting Deck
Brooklyn Indie Games: Fate Accelerated 1 (2014 Pack)

OmegaZone Setting Guide
Brooklyn Indie Games: Fate Accelerated 1 (2014 )
Brooklyn Indie Games: Fate Accelerated 1 (2014 )

Omens of War
Fantasy Flight Games: Warhammer Fantasy Roleplay 3 (2011 Box)

Omens of War: Advanced Combat and Warriors
Fantasy Flight Games: Warhammer Fantasy Roleplay 3 (2011 PDF)

Omlevex
Z-Man Games: Mutants & Masterminds 1 (2003 )

Omni System
Morrigan Press: Omni System 1 (2005 )

Omnifray RPG Expert Manual
Self-published: Omnifray 1 (2009 )

Omnifray: Basic Handbook
Lulu: Omnifray 1 (2008 )

Omnigon
Omnigon Games: Omnigon 1 (1989 )

Omnigon: The Alien Analog
Omnigon Games: Omnigon 1 (1989 )

On Display
Paracelsus Games: Generic / One-Off System 1 (2015 PDF)

On Hallowed Ground
TSR: AD&D 2 (1996 )

On Her Majesty's Arcane Service
Flying Mice: StarCluster / Starpool 2.5 (2009 )

On Her Majesty's Secret Service
Victory Games: James Bond 007 1 (1987 Box)

On Location
Atlas Games: Feng Shui 1.5 (2002 )

On Silver Wings
Paradigm Concepts: Witch Hunter 1 (2010 )

On the Nature of Davokar
Järnringen: Symbaroum 1 (2015 PDF)

On the Rocks
Pinnacle: Savage Worlds 1 (2003 PDF)

On The Run
FanPro: Shadowrun 4 (2006 )

On the Verge
TSR: Fiction (1998 )

Once Men
Chaosium: Call of Cthulhu 6 (2008 )

Once More Unto the Breach: The Movie Era Sourcebook
Self-published: ICON 1 (2001 PDF)

Once Upon a Time
Avalon Game Company: d20 Modern 1 (2010 PDF)

Once Upon a Time in the Far West
Adamant Entertainment: Generic 1 (2012 eBook)

Once Upon An Apocalypse
Chaosium: Fiction (2014 )

One Can Have Her
Self-published: One Can Have Her 1 (2005 PDF)

One Crowded Hour
Comstar Games: Traveller / Mongoose 1 (2008 PDF)
Avenger Enterprises: Traveller / Mongoose 1 (2008 PDF)
Mongoose Publishing: Traveller / Mongoose 1 (2008 PDF)

One Dark Night in Weeping Briar
Wizards of the Coast: Dungeons & Dragons 4 (2009 )

One Foot in the Grave
Creepy Doll Studios: Custom 1 (2013 PDF)

One for the Money
Pelgrane Press: Cthulhu Confidential 1 (2017 PDF)

One Hundred and Thirty Guns
Dakkar Unlimited: Inverted 20 1 (2009 PDF)

One Last Riddle
Wizards of the Coast: Dungeons & Dragons 3 (2001 PDF)

One Man's Garbage
RPGObjects: d20 Modern 1 (2005 PDF)

One Man's Garbage... Another Man's Treasure
RPGObjects: d20 Modern 1 (2009 )

One Million Magic Items
Adamant Entertainment: d20 3.5 (2007 PDF)

One Night Stands: "The Orlando Adventures"
Tri-City Games: SuperBabes 1 (1994 )

One o'Clock Wake-Up
Arc Dream Publishing: Godlike 1 (2003 PDF)

One of the Living
Eden Studios: Unisystem (2004 )
Eden Studios: Unisystem (2005 )

One of Those Nights
Lone Delver Games: Tunnels & Trolls 7.5 (2010 PDF)

One on One Adventures Compendium
Expeditious Retreat Press: Pathfinder 1 (2009 PDF)

The One Page Dungeon Codex 2009
Self-published: Generic 1 (2009 PDF)

One Page Dungeon Compendium
Self-published: Generic 1 (2009 PDF)

The One Ring Core Rules
Free League Publishing: Generic 1 (2021 Hardcover)

One Ring Dice Set
Cubicle 7 Entertainment: One Ring 1 (2012 Box)

The One Ring: Adventures over the Edge of the Wild
Cubicle 7 Entertainment, UK: One Ring 1 (2014 Hardcover)
Cubicle 7 Entertainment, UK: One Ring 1 (2011 Box)

One Shots
Atlas Games: Unknown Armies 1 (1999 )

One Stage Before
FASA Corporation: Shadowrun 2 (1992 )

One Thousand Faces: Villains & Scoundrels
Citizen Games: d20 3 (2002 )

The One Who Watches From Below
Goodman Games: Dungeon Crawl Classics 1 (2014 )

One-Act Adventure: Vengeance by Proxy
Samardan Press: Traveller / Mongoose 1 (2009 )

One-Page Romps: A Simple Request
Genius Loci Games: D&D / OSR 1 (2014 Looseleaf)

Only Acrobats Need Apply
Self-published: d20 3.5 (2013 PDF)

Only War
Fantasy Flight Games: Only War 1 (2012 Hardcover)

Only War Game Master's Kit
Fantasy Flight Games: Only War 1 (2012 )

ONS1: The Jungle Ruins of Madaro-Shanti
Frog God Games: Swords & Wizardry 1 (2011 )
Frog God Games: Pathfinder 1 (2011 )

ONS2: Death in the Painted Canyons
Frog God Games: Swords & Wizardry 1 (2011 )
Frog God Games: Pathfinder 1 (2011 )

ONS3: The Spire of Iron and Crystal
Frog God Games: Swords & Wizardry 1 (2011 )
Frog God Games: Pathfinder 1 (2011 )

ONS4: Dread Saecaroth
Frog God Games: Pathfinder 1 (2012 )
Frog God Games: Swords & Wizardry 1 (2012 )

Onslaught at Arda I
Fantasy Flight Games: Age of Rebellion 1 (2014 Hardcover)

OP1: Tales of the Outer Planes
TSR: AD&D 1 (1988 )

Open Core Core Rules
Battlefield Press: Open Core 1 (2005 )

Open Game Table: The Anthology of Roleplaying Game Blogs, Volume 2
Self-published: Generic 1 (2010 )

Open Game Table: The Anthology of Roleplaying Game Blogs, Volume I
Self-published: Generic 1 (2009 )

Open Gaming Bazaar #1
E. W. Morton: d20 3.5 (2006 PDF)

The Open Gaming Bazaar #2
E. W. Morton: d20 3.5 (2006 PDF)

The Open Gaming Bazaar #3
E. W. Morton: d20 3.5 (2007 PDF)

Open Grave: Secrets of the Undead
Wizards of the Coast: Dungeons & Dragons 4 (2009 Hardcover)

Opener of the Ways
Triple Ace Games: Savage Worlds 2 (2010 PDF)

Opening Salvo
Margaret Weis Productions: Dragon Brigade 1 (2011 )

Opening The Dark
Mob United Media: Generic / One-Off System 1 (2007 )

OpenQuest
D101 Games: OpenQuest 1 (2009 )

OpenQuest 2nd Edition Deluxe
D101 Games: OpenQuest 2 (2013 )

OpenQuest Basic Edition
D101 Games: OpenQuest 2 (2014 Digest)

OpenQuest
D101 Games: OpenQuest 1 (2009 eBook)
D101 Games: OpenQuest 1 (2010 )
D101 Games: OpenQuest 1 (2010 )

Operation Crouching Dragon
GDW: Twilight: 2000 2 (1992 )

Operation Dead Drop
OtherWorld Creations: d20 Modern 1 (2003 PDF)

Operation Dominoes 1: Moonshadow
Comstar Media: Generic 1 (2006 PDF)
Avenger Enterprises: Generic 1 (2006 PDF)

Operation Dominoes 2: The Minds of Idsur
Comstar Media: Generic 1 (2007 PDF)
Avenger Enterprises: Generic 1 (2007 PDF)

Operation Dominoes 3: The Isdur Gambit
Comstar Media: Generic 1 (2007 PDF)
Avenger Enterprises: Generic 1 (2007 PDF)

Operation Dominoes 4: The Iskyar Metamorphosis
Comstar Media: Generic 1 (2008 PDF)
Avenger Enterprises: Generic 1 (2008 PDF)

Operation Hydra
Bedrock Games: Terror Network 1 (2010 )

Operation Ogre
Judges Guild: D&D / Original 1 (1979 )

Operation Overlord
3W: Traveller: 2300 2 (1989 )

Operation Peregrine
Fantasy Games Unlimited: Space Opera 1 (1983 )

Operation Seven Swords
Leading Edge Games: Phoenix Command 1 (1987 )

Operation Tunnel RAT
SteamPower Publishing: d20 Modern 1 (2007 PDF)

Operation Ulysses
Chaosium: BRP 2 (2011 )

Operation Winter Kill
OtherWorld Creations: d20 Modern 1 (2004 PDF)

Operation: Atlantis
Mayfair Games: DC Heroes 1 (1988 )

Operation: Bookbinder
Vigilance Press: Icons 1 (2010 PDF)

Operation: Elrood
West End Games: Star Wars d6 2 (1996 )

Operation: Fallen Reich
Fallen Publishing, UK: Generic / One-Off System 1 (2009 Hardcover)

Operation: Fallen Reich Life Board
Fallen Publishing, UK: Generic 1 (2009 Box)

Operation: Hard Sell
West End Games: Torg 1 (1991 )

Operation: Hitler
Rapport Games: Morpheus 1 (1990 )

Operation: Nightside
West End Games: MasterBook 1 (1997 )

Operation: Perfect Blue
Cutter's Guild Games: Perfect Blue (2002 )

The Operations Division
Modiphius Entertainment: Star Trek 2d20 1 (2018 Hardcover)

Opponents Unlimited
Fantasy Games Unlimited: Villains and Vigilantes 2 (1982 )

The Oracle
Open Design: Pathfinder 1 (2011 PDF)

Oracle Curses
Above Average Creations: Pathfinder 1 (2011 PDF)

Oracle of Orcas
Alea Publishing Group: Dungeons & Dragons 4 (2009 PDF)

Additional Oracle Curses
Super Genius Games: Pathfinder 1 (2010 PDF)
OtherWorld Creations: Pathfinder 1 (2010 PDF)

The Orb of Xoriat
Wizards of the Coast: Fiction (2005 )

Orb Quest
Metagaming: The Fantasy Trip 2 (1982 )

Orbaal
Columbia Games: Generic (1987 )

The Orbas Lode
Rus Games, Australia: Rus 1 (1991 )

Orbis Mundi
Phalanx Games Design: d20 3.5 (2006 PDF)

Orbit
6-0 Games: Orbit 1 (1998 )

Orbital
Zozer Games: Traveller / Mongoose 1 (2012 )
Zozer Games: Cepheus Engine 1 (2016 )

ORC Combat Cards: Street Combat Set
Vajra Enterprises: ORC 1 (2004 PDF)

Orc Fortress
0one Games: Generic 1 (2006 PDF)

The Orc King
Wizards of the Coast: Fiction (2007 Hardcover)
Wizards of the Coast: Fiction (2008 )

Orc's Lair
Destination Games: Generic 1 (1996 Digest)

Orcbusters
West End Games: Paranoia 1 (1986 )

Orcfest
Fast Forward Entertainment: d20 3 (2002 )

Orcmark
Triple Ace Games: Savage Worlds 2 (2010 PDF)

Orcs of Golarion
Paizo Publishing: Pathfinder 1 (2010 )

Orcs of the Eternal Zenith
Raging Swan Press: Pathfinder 1 (2011 PDF)

Orcs of the High Mountains
Dark City Games: Legends of the Ancient World 1 (2006 PDF)

Orcs of the Scarlet Sail
Anti Paladin Games: Generic 1 (2009 PDF)

Orcs: A New Player Character Race and Much More!
Troll in the Corner: Pathfinder 1 (2010 PDF)

Orcslayer
Steve Jackson Games: GURPS 1 (1985 )

Orcus Journal
Frog God Games: Generic 1 (2012 )

The Ordan Valley
Black Wyvern Press: Labyrinth Lord 2 (2011 PDF)

Ordeal by Eshaar
FASA Corporation: Traveller 1 (1981 )

Order Book: Michaelites
Sword & Sorcery: d20 3 (2003 )

The Order of Hermes
Lion Rampant: Ars Magica 2 (1990 )

Order of Hermes Tradition Book
White Wolf Publishing: Mage: The Ascension 2 (1997 )

The Order of Reason
ArtHaus: Mage: The Sorcerers Crusade 1 (2001 )

The Order of the Gilded Rose
Adamant Entertainment: d20 3.5 (2005 PDF)

The Order of the Stick: Don't Split the Party
Giant in the Playground: Fiction (2009 )

The Order of the Stick: Dungeon Crawlin' Fools
Giant in the Playground: Fiction (2005 TPB)

The Order of the Stick: No Cure for the Paladin Blues
Giant in the Playground: Fiction (2006 TPB)

The Order of the Stick: On the Origin of PCs
Giant in the Playground: Fiction (2005 TPB)

The Order of the Stick: Start of Darkness
Giant in the Playground: Fiction (2007 )

The Order of the Stick: War and XPs
Giant in the Playground: Fiction (2008 )

Orders of Solomon
Paradigm Concepts: Witch Hunter 1 (2010 )

Ordo Draconis #1
Magnum Opus Press: Dragon Warriors 1.1 (2009 PDF)

Ordo Dracul
White Wolf Publishing: Vampire: The Requiem 1 (2005 Hardcover)

Ordo Nobilis: Mythic Europe's Nobility
Atlas Games: Ars Magica 4 (2000 )

Organization Book 1
BTRC: CORPS 1 (1992 )

Organized Crimes
Fantasy Games Unlimited: Villains and Vigilantes 2 (1985 )

The Orgillion Horror
I.C.E.: Rolemaster 2.5 (1989 )
I.C.E.: HERO 3 (1989 )

Oriental Adventures
TSR: AD&D 1 (1985 Hardcover)
Twenty-First Century Games: AD&D 1 (1999 )

Oriental Adventures
Wizards of the Coast: Dungeons & Dragons 3 (2001 Hardcover)

Origin of the Species: Classic Fantasy
Crafty Games: Spycraft 2 (2008 PDF)

Origin of the Species: Light of Olympus
Crafty Games: Spycraft 2 (2007 PDF)

Origin of the Species: Transmechs
Crafty Games: Spycraft 2 (2009 PDF)

Original Adventures Reincarnated #1: Into the Borderlands
Goodman Games: Dungeons & Dragons 5 (2018 Hardcover)

Original Adventures Reincarnated #2: The Isle of Dread
Goodman Games: Dungeons & Dragons 5 (2018 Hardcover)

Original Adventures Reincarnated #3: Expedition to the Barrier Peaks
Goodman Games: Dungeons & Dragons 5 (2019 Hardcover)

Original Adventures Reincarnated #4: The Lost City
Goodman Games: Dungeons & Dragons 5 (2020 Hardcover)

Original City State Map Collectors Edition
Judges Guild: Generic 1 (1978 Looseleaf)

Original Dungeons & Dragons
Wizards of the Coast: D&D / Original 1 (2013 Box)

Original Edition Characters
Goblinoid Games: Labyrinth Lord 2 (2008 )

Original Edition Delta: Book of Spells
Self-published: D&D / Original 1 (2009 Digest)

Original Edition Delta: Book of War
Self-published: Book of War 1 (2011 Digest)

Original Edition Options: Cavalier, Paladin & Squire
Brave Halfling Publishing: D&D / Original 1 (2009 PDF)

Original Edition Options: The Halfling Adventurer
Brave Halfling Publishing: D&D / Original 1 (2009 PDF)

The Original, Revised and Expanded Tegel Manor
Gamescience: Generic 1 (1989 )

Origins of Bureau 13: The Black Powder Years
Tri Tac Games: Bureau 13 3 (2002 PDF)

Origins of the Specious
Mongoose Publishing: Generic 1 (2009 )
Postmortem Studios: Generic 1 (2009 )

Orion Ruse
FASA Corporation: Star Trek 1 (1984 )

The Orions
FASA Corporation: Star Trek 2 (1987 )

The Ork Nation of Cara Fahd
FASA Corporation: Earthdawn 1 (1998 )

Ork! The Roleplaying Game
Green Ronin Publishing: Generic / One-Off System 1 (2000 )

Orks: Children of Pain
John Wick Presents: Pathfinder 1 (2012 PDF)

Orkworld
Wicked Press: Orkworld 1 (2000 )

Orlanth is Dead!
Issaries: Hero Wars 1 (2002 )

The Orphan-Grinders
White Wolf Publishing: Storyteller System: World of Darkness 3 (2004 )

Orphaned Races: Ascorbites and Hironem
Holistic Design: Fading Suns 2 (2003 )

The Orphans Survival Guide
White Wolf Publishing: Mage: The Ascension 2 (1998 )

Orpheus
White Wolf Publishing: Storyteller System: World of Darkness 3 (2003 Hardcover)

Orrorsh
West End Games: Torg 1 (1991 )

Orschild: Winds of War
Cell Entertainment: Gemini 1 (1999 )

ORX: Nasty, Brutish & Short
Wild Hunt Studios: ORX 1 (2006 )

OS1: Something Unholy Stirs
Sacrosanct Games: OSRIC 2 (2010 PDF)

Osirion, Land of Pharaohs
Paizo Publishing: d20 3.5 (2008 )

The Osiris Chip
Atlas Games: Cyberpunk (1992 )

OSR Bonus Cards: Fantasy Deck #1
Small Niche Games: D&D / OSR 1 (2010 PDF)

O.S.R.I.C. First Edition
Self-published: O.S.R.I.C. First Edition (2006 PDF)
Self-published: OSRIC 1 (2007 PDF)

O.S.R.I.C. Second Edition
First Edition Society: O.S.R.I.C. Second Edition 2 (2009 )
First Edition Society: OSRIC 2 (2009 )
First Edition Society: OSRIC 2 (2009 Hardcover)
First Edition Society: OSRIC 2 (2009 Hardcover)

OSRIC Psionic Combat
Dragoneer Publishing: OSRIC 2.2 (2011 PDF)

OSRIC Unearthed
Ronin Arts: OSRIC 1 (2007 )

OSRIC v2.00
Self-published: OSRIC 2 (2008 PDF)

Ostmark
Triple Ace Games: Savage Worlds 2 (2010 PDF)

Othello
LPJ Design: d20 3.5 (2005 PDF)

Other Dust
Sine Nomine Publishing: Other Dust 1 (2012 )
Sine Nomine Publishing: Other Dust 1 (2012 Hardcover)

Other Suns
Fantasy Games Unlimited: BRP 1 (1983 )

Other Worlds
Signal 13: Other Worlds 1 (2011 PDF)

Otherkind
Lumpley Games: Generic / One-Off System 1 (2002 PDF)

Otherspace
West End Games: Star Wars d6 1 (1989 )

Otherspace II: Invasion
West End Games: Star Wars d6 1 (1989 )

Otherverse America Campaign Setting
Skortched Urf' Studios: Generic 1 (2009 PDF)

The Otherwhere Quest
Mayfair Games: DC Heroes 2 (1990 )

Otosan Uchi
AEG: Legend of the Five Rings 1 (2000 Box)

Oubliette #9: Mini-adventures, spells, magic items, monsters and more...
Self-published: Labyrinth Lord 2 (2015 Digest)

Our American Cousins
Cubicle 7 Entertainment: Call of Cthulhu 7 (2017 )

Our Friends the Machines & Other Mysteries
Free League Publishing, UK: Year Zero 1 (2018 Hardcover)

Our Ladies of Sorrow
Miskatonic River Press: Call of Cthulhu 6 (2009 )

Our Lady of Silver
Paizo Publishing: d20 3.5 (2009 PDF)

Our Last Best Hope
Magpie Games: Last Best Hope 1 (2012 )

Our Last Best Hope Expansion Book
Magpie Games: Last Best Hope 1 (2013 )

Out for Blood
Bastion Press: d20 3.5 (2003 )
Bastion Press: d20 3.5 (2005 PDF)

Out in the Black
Margaret Weis Productions: Serenity 1 (2006 )

Out of Body, Out of Mind
AEG: d20 3 (2000 )

Out of Dodge
Bully Pulpit Games: LARP / One-Off 1 (2014 )

Out of Nippon
West End Games: Fiction (1992 )

Out of Space
Pelgrane Press: Trail of Cthulhu 1 (2013 )

Out of the Abyss
Death's Edge Games: Inferno 1 (1995 )

Out of the Abyss
Wizards of the Coast: Dungeons & Dragons 5 (2015 Hardcover)

Out of the Dark
Shield Games: Fifth Cycle 1 (1990 )

Out of the Mists
Star Childe Publications: Justifiers 1 (1989 )

Out of the Pit
Puffin Books: Fighting Fantasy 1 (1989 )
Cubicle 7 Entertainment: Advanced Fighting Fantasy 2 (2011 )
Arion Games: Advanced Fighting Fantasy 2 (2011 )

Out of the Shadows
Corgi Books, UK: Dragon Warriors (1986 )

Out of the Vaults
Sword & Sorcery: d20 Modern 1 (2004 )

Out of the Violent Planet
Self-published: Reign 1 (2011 PDF)

Out of the Woods
Pelgrane Press: Trail of Cthulhu 1 (2017 )

Out of Time
Pelgrane Press: Trail of Cthulhu 1 (2011 )

Out There
Indie Game Design Company #2: Out There 1 (2009 PDF)

Outbound: An Explorer's Guide
TSR: Alternity 1 (1999 )

Outbreak at Hopewell
Daring Entertainment: Savage Worlds 2 (2010 PDF)

Outbreak!
6d6Fireball.com: 6d6 Core 1 (2011 )

Outbreak!
6d6, UK: 6d6 2 (2014 )

Outbreak: Undead
Hunters Books and Apparel: Outbreak: Undead 1 (2010 Hardcover)

The Outcast
TSR: Fiction (1993 )

The Outcaste
White Wolf Publishing: Exalted 1 (2004 )

The Outcasts
FASA Corporation: Star Trek 2 (1985 )

Outcasts: A Players Guide to Pariahs
White Wolf Publishing: Storyteller System: World of Darkness 1 (1995 )

Outdoor Geomorphs Set One: Walled City
TSR: Generic 1 (1977 )

Outdoor Mapping Sheets
Troll Lord Games: Generic 1 (2009 Looseleaf)

The Outer Presence
Kort'thalis Publishing: Outer Presence 1 (2015 )
Kort'thalis Publishing: Outer Presence 1 (2015 )

The Outer Reach
Fantasy Flight Games: Deathwatch 1 (2012 Hardcover)

Outer Veil
Spica Publishing: Traveller / Mongoose 1 (2011 PDF)

Outer Veil Sector Map
Spica Publishing: Traveller / Mongoose 1 (2011 PDF)

Outer-Rim System
New Dimension Games: Starquest 1 (2005 )

Outgunned
Two Little Mice: Director's Cut (2023 Hardcover)
Free League Publishing: Director's Cut (2023 Hardcover)
Two Little Mice: Generic 1 (2023 Hardcover)

Outland - Adventure System Gazetteer
Idyll Creations: Adventure System 3 (2021 PDF)

Outlaw
I.C.E.: Rolemaster 2.5 (1991 )
I.C.E.: Space Master 2 (1991 )

Outpost 19
Chaosium: BRP 2 (2008 PDF)

Outpost Mars
Zozer Games: Traveller / Mongoose 1 (2012 )

Outpost of the Ogre Overlord
PinHammer: AD&D 1 (2010 PDF)

Outpost Qether
OtherWorld Creations: d20 3 (2001 PDF)
OtherWorld Creations: RuneQuest / Mongoose 1 (2006 PDF)

Outremer
Flying Mice: StarCluster / Starpool 3 (2011 )

Outside Standard Channels
Clockworks: Spookshow (1999 )

The Outworlds: A Starsector Atlas
Fantasy Games Unlimited: Space Opera 1 (1986 )

OVA: Open Versatile Anime Role-Playing Game
Wise Turtle: OVA 1 (2006 )

OVA: The Anime Role-Playing Game
Wise Turtle: OVA 2 (2015 Digest)

Over the Edge
Atlas Games: Over the Edge 1 (1992 )
Atlas Games: Over the Edge 2 (1997 )

Over the Edge
Wizards of the Coast: Dungeons & Dragons 3 (2004 HTML)

Over the Edge
Atlas Games: Over the Edge 3 (2019 Hardcover)
Atlas Games: Over the Edge 2 (2012 Hardcover)

Over The Edge Dice Set
Atlas Games: Over the Edge 3 (2018 Pack)

Over The Edge Dice Set
Atlas Games: Over the Edge 3 (2019 Pack)

Over the Misty Mountains Cold
I.C.E.: Lord of the Rings Adventure / MERP 1 (1993 )

Overkill
Flying Buffalo: Tunnels & Trolls 4 (1977 )
Flying Buffalo: Tunnels & Trolls 5 (1980 )
Chris Harvey, UK: Tunnels & Trolls 5 (1980 )

Overlight
Renegade Game Studios: Overlight 1 (2018 Hardcover)

The Overseer
White Wolf Publishing: Fiction (2003 )

Overtime
Maverick Games Co.: Hunt 1 (1992 )

Owl Hoot Trail
Pelgrane Press: Microlite20 1 (2013 )

Oz: Dark and Terrible
Emerald City Expeditions: Generic / One-Off System 1 (2010 Hardcover)