There are scores of different independent RPG systems out there that are released under the Wizards of the Coast (WotC) Open Game License (OGL), which itself came out in 2000.
Most of these game systems re-interpreted the OGL rules in some manner or other, codifying them in more detail than the OGL itself spelled out. These are usually called "System Resource Documents" (SRDs).
This means that while the game systems are built on the same framework, the actual rules may vary. Mixing-and-matching supplements between the different SRDs generally requires some level of conversion. (e.g. converting a D&D 3.0 module to Pathfinder).
Some of these systems have really pushed the OGL in very different directions. (e.g. Mutants & Masterminds)
This is not a complete list, but these are some OGL game systems that I am familiar with, in the order in which they came to mind...
- Dungeons & Dragons (3rd edition; 3rd edition revised; 5th edition)
- Pathfinder Role Playing Game
- Starfinder Role Playing Game
- d20 Modern
- Mutants & Masterminds
- True 20
- Swords & Wizardry
- Lamentations of the Flame Princess
- Dungeon Crawl Classics
- Castles & Crusades
- 13th Age
- Gamma World (6th edition)
Again, not nearly a complete list... just the ones I thought of off the top of my head.
|David knott 242|
Yes, please don't forget Monte Cook's Arcana Unearthed / Arcana Evolved , as that remains my favorite version of d20.
A few others that have gone unmentioned:
Monte Cook Presents: Iron Heroes
Conan the Roleplaying Game (OGL version by by Mongoose Publishing)
Eclipse: The Codex Persona
Call of Cthulhu d20
Big Eyes, Small Mouth d20
Swashbuckling Adventures (7th Sea for d20)
World of Warcraft: The Roleplaying Game
Trailblazer: New Horizons in 3.5 Roleplaying
Legend (the one by Rule of Cool games)
There were also a large number of 3rd party D&D settings that changed so much about the core mechanics you might as well consider them separate, but compatible RPGs, such as:
Nyambe, African Adventures
WarCraft the Roleplaying Game (The D&D branded 1st edition of the WoW RPG)
Iron Kingdoms (the first edition was d20/OGL)
...and probably a lot more I don't own or haven't played.