Here is a big list of all the game systems we have and know at least something about.

 

Engel, Scion, d20 Modern, DC Adventures, Savage Worlds, Marvel Universe RPG, nWoD: Core, Vampire the Requiem, Werewolf the Forsaken, Mage the Awakening, Changeling the Lost, Geist the Sin-Eaters, Demon the Descent, oWoD: Demon the Fallen, Vampire the Dark Ages, Wraith the Oblivion, Mage the Ascension, Pathfinder, Dungeons and Dragons 3.5, 4,and 5th editions, Shadowrun all editions, Dungeons and Dragons Rules Cyclopedia, Immortal the Invisible War(first edition), Noctum, Champions: new Millennium, Star Frontiers, Earthdawn all editions, Cyberpunk 2020, Dresden Files, d20 Judge Dredd, Palladium Teenage Mutant Ninja Turtles, TORG, Marvel Superheroes (FASERIP), Deadlands 1st and 2nd editions, Little Fears, Forbidden Kingdoms, In Nomine, Legend of the 5 Rings, GURPS, Many of the Minds Eye Theatre Games, Apocalypse World, Burning Wheel, Call of Cthulhu, Doctor Who Adventures, Doctor Who RPG, Eclipse Phase, Exalted 2nd Edition, Free Market, Mutant and Masterminds, Blades in the Dark, Part-Time Gods and Red Dwarf

If we get new ones this list will be updated.