The roleplaying system which first appeared in Dungeons & Dragons 3E.
The term 'd20 System' is a trademark of Wizards of the Coast.
- 13th Age ● 'This is the home of the 13th Age / Archmage Engine system reference document. It contains all the open content from the 13th Age RPG – the Archmage Engine.'
- Alchemy System ● A modified d20 game set in its own universe.
- Animalball Melee ● A simplified d20 System for gladiatorial combat.
- Basic Fantasy Role-Playing Game ● A fusion of Basic D&D with D&D 3E to create a simple, light-weight game.
- Blue Rose ● A d20-based RPG.
- Contagion ● A free wargame.
- Core Elements ● A distillation of the d20 System in just seven pages.
- d20 Anime ● Play magical girls, sorcerers and mecha pilots using everyone's favourite system.
- d20 Modern ● Modern role-playing, from occult investigation to special ops and anything in between.
- d20 Open Mass Combat System ● A free wargame.
- Dan's Diminutive D20 ● Quick and easy d20 role-playing.
- Dungeons & Dragons 3E ● The third edition of the world's most popular roleplaying game.
- E6 ● The game inside Dungeons & Dragons.
- Microlite20 ● A simplified version of the d20 System.
- MULRAH ● An RPG that has undergone considerable changes in recent versions.
- Pathfinder ● A role-playing game based on Dungeons & Dragons 3.5.
- PCGen ● A character generator for the d20 System.
- Perfect20 ● A variant on D&D 3e.
- Prometheus SRD ● An open version of the character creation and advancement rules from Dungeons & Dragons 3E.
- Raven Crowking's Fantasy Game ● Raven Crowking's reworking of Dungeons & Dragons
- Simple 20 ● A simple d20-based RPG.
- Spellchrome ● A classless version of the d20 System.
- Sweet20 ● Bringing indie sensibilities to the d20 System.
- Tech Noir ● A cyberpunk game that uses a d20.
- True20 ● A d20-based RPG.
- Green Ronin Publishing ● An RPG publisher.