Unearthed Arcana
From Dungeons and Dragons Wiki
There are two books with this name about variant rules:
- Unearthed Arcana for AD&D 1st Edition
- Unearthed Arcana for D&D 3rd Edition
- Unearthed Arcana (5e) - Series of PDFs of unofficial/playtest rules for D&D 5th Edition
See also:
- Arcana Unearthed a variant players handbook written by Monte Cooke