- OutOfTheBit Ltd
- One Legged Seagull
- One Hamsa
- Outhouz, Inc.
- Outsmart
- ON3D
- Otherworld Interactive
- Outerlight Ltd.
- Odd Meter
- Old School Blender Addicted
- Old Shack Studio
- onebraverobot
- OnionMilk
- OrtiGames/OrtiSoft
- Oscar Ortigueira López
- Out Of Bounds
- Orrery Games
- Outer Planet Studios
- Outgunned Games
- Origin8 Technologies Ltd
- Oliver Peat
- Olympic
- Outrage Entertainment
- OVERKILL - A Starbreeze Studio