The rules of 1st and 2nd edition AD&D.
Typically Open Game License.
The original rules are not open.
- For Gold & Glory ● A retroclone of 2E AD&D.
- Labyrinth Lord ● A retroclone of Basic/Expert D&D.
- Myth & Magic ● An adaptation of 2E AD&D.
- OSRIC ● A retroclone of 1st Edition Dungeons & Dragons.
- Tales of the Grotesque and Dungeonesque ● Horror role-playing resource.
- World of Nevermore ● A setting for Advanced Dungeons & Dragons.