Starts with the letter 'O'
- Oblique. Variant with board with 40 squares turned 45 degrees. (Cells: 40) By Tony Quintanilla.
- Oblong Chess 44. Variant of Oblong Chess on board with 44 squares. (4x11, Cells: 44) By Erez Schatz.
- Once More, with Deans. Subvariants of River-with-university-and-cathedral series with extra piece type. By Charles Gilman.
- The One Ring. White wants to get the Ring to the far side and destroy it. (5x8, Cells: 42) By Robert Price.
- Onitama. Cards decide how pieces move, perfect information with no chance beyond setup. Author: Mikk . Inventor: Shimpei Sato.
- Outer Space Chess. Space-themed game with hyperspace and regular space boards. (5x8x2, Cells: 43) By Nicholas Kuschinski.
Total items listed: 6