| Origo Games | Publisher | |
| Orihaus | Developer | |
| Orikami | Developer | |
| Oriol | Developer | |
| Orion | Developer | |
| Orion Game Studio | Developer | |
| Orion Games | Developer | |
| Orion Interactive | DeveloperPublisher | |
| Orion Software | DeveloperPublisher | |
| OrionDark7 | Developer | |
| OrionGD | Developer | |
| Orion_ | Developer | |
| OrkybitGames | Developer | |
| Orla | Developer | |
| Orlando Araujo | Developer | |
| OrlandoIsSoCool | Developer | |
| Ornith | Developer | |
| Ornithopter Games | Developer | |
| Oro | Developer | |
| Orpheck Inc. | Developer | |
| Orpheus | DeveloperPublisher | |
| Orpheus (Richard Wilkins, Geoff M. Phillips) | Developer | |
| Orpheus Software | Publisher | |
| Orrin | Developer | |
| Orsailius | Developer | |
| Orthogonal Games | Developer | |
| Orube Game Studio | DeveloperPublisher | |
| OsXurelazos | Developer | |
| Osarion | Developer | |
| Osaris Games | Developer | |
| Osariusz | Developer | |
| Oscar | Developer | |
| Oscar Arcane | Developer | |
| Oscar Brittain | Developer | |
| Oscar Celestini SHOP | Developer | |
| Oscar Cerro | Developer | |
| Oscar Chu | Developer | |
| Oscar Daudt Neto | Developer | |
| Oscar Gao | Developer | |
| Oscar Kenneth Albero Ingles | Developer | |
| Oscar Mordue | Developer | |
| Oscillatingcabbage | Developer | |
| Oshaberi | Developer | |
| Oshisaure | Developer | |
| Osiris Studios | Developer | |
| Oskar van Velden | Developer | |
| OskarDev | Developer | |
| OskarNystrom | Developer | |
| Oskarnik | Developer | |
| Oskarros | Developer | |