The Dungeon Crawl Classics Role Playing Game is named after Goodman's popular line of modules. While inspired by old school versions of D&D (the "Appendix N" in the blurb below is a reference to the bibliography in AD&D's DMG), DCC is not closely derived from any of them. The core mechanic relies on Zocchi dice, like d7s; and the the abilities, the range of scores, and the classes and races are familiar. From Goodman's website:

Glory & Gold Won by Sorcery & Sword

You’re no hero.

You’re an adventurer: a reaver, a cutpurse, a heathen-slayer, a tight-lipped warlock guarding long-dead secrets. You seek gold and glory, winning it with sword and spell, caked in the blood and filth of the weak, the dark, the demons, and the vanquished. There are treasures to be won deep underneath, and you shall have them.

Return to the glory days of fantasy with the Dungeon Crawl Classics Role Playing Game. Adventure as 1974 intended you to, with modern rules grounded in the origins of sword & sorcery. Fast play, cryptic secrets, and a mysterious past await you: turn the page…

Rules Set: DCC RPG, an OGL system that cross-breeds Appendix N with a streamlined version of 3E.