Starts with the letter 'O'
- Odds Chess. Ways of giving a weaker opponent better odds. (8x8, Cells: 64) Author: Roger Cooper.
- Official Football Chess. Variant from the 1960's with pieces replaced by football players. (8x8, Cells: 64) Author: Hans L. Bodlaender.
- Orda Chess. Asymmetric variant where one army has pieces that move like knights but capture differently. By Daniel Lee.
- OverKnight Chess. Pawns are replaced by Knights, which promote. (8x8, Cells: 64)
|4 'Game' entries listed||2 'Each player has a different army' entries listed|
|1 'Sold commercially' entry listed|
Total items listed: 4