Starts with the letter 'O'
- Objective Bastardo. Cut-throat four-player variant where each player has a secret objective.
- Once More, with Deans. Subvariants of River-with-university-and-cathedral series with extra piece type.
- Orwell Chess. Three player variant themed on George Orwell's 1984. (7x12, Cells: 84)
- Orwell Chess . Three player variant themed on George Orwell's 1984.
Total items listed: 4