NEMESIS: Roleplaying in Worlds of Horror is a horror roleplaying game, inspired by the works of H. P. Lovecraft, Stephen King, Ambrose Bierce, Brian Lumley, and William Peter Blatty. It was also inspired by Gilchrist Trust, and the Call of Cthulhu setting Delta Green, which Dennis Detwiller co-authored.

The system is designed by Greg Stolze, who combined elements from two of his previous works: the One-Roll Engine (originally seen in Godlike), and the Madness Meters from Unknown Armies.

NEMESIS was published using the "ransom" method, and released as a free PDF once the target of USD$1,000 in pledges was reached (which took about a week).