Starts with the letter 'O'
- Octa-Ashtapada. 8x8x8 variant with powerful armies and the potential for multiple royal pieces per side. By Larry L. Smith.
- Octopus Chess . Featuring the Octopus, the Sorcerer Snake, the Ferz Knight, the Wazir Knight and the Ninja Pawns. By Charles Daniel.
- Odin's Rune Chess . Missing description Author: Michael Nelson. Inventor: Gary K. Gifford.
- Omega chess . Commercial chess variant on board with 104 squares. Author: David Howe.
- Omega Chess Extended . Missing description By Mykola Dolgalov.
- Omega Transplant . The Warmachine Alfil , the Camel Ferz, the Ninja Pawns and the usual suspects battle it out on a new chessboard. By Charles Daniel.
- Open Chess . Large variant with few pawns. Author: Marek14 . Inventor: Moses Snell-Feikema.
- Operational Chess. Wargame inspired variant played on a wide board. By Andy Thomas.
- Operational Chess 2. Large, wargame inspired variant with ranged pieces. By Andy Thomas.
- Opulent Chess . Zillions file for Opulent Chess. By Greg Strong.
- Orwell Chess . Three player variant themed on George Orwell's 1984. By Glenn Overby II.
- Outback Chess . New pieces on plus-shaped board. Author: Peter Aronson. Inventor: Timothy R. Newton.
Total items listed: 12