- Octodad: Dadliest Catch
- Octopus City Blues
- Odallus: The Dark Call
- Oddworld: New 'n' Tasty!
- Oedipus/Antigone
- Offspring Fling!
- Offworld Trading Company
- Offworld Trading Company: Interdimensional
- Offworld Trading Company: Jupiter's Forge
- Offworld Trading Company: The Ceres Initiative
- Ogre [II/2017]
- Oh...Sir! The Hollywood Roast
- Oh...Sir! The Insult Simulator
- Oil Rush
- OIO: The Game
- Okhlos
- Old Man's Journey
- Old World
- Old World: Heroes of the Aegean
- Oliver & Spike: Dimension Jumpers
- OlliOlli
- OlliOlli 2: Welcome to Olliwood
- Olympia Rising
- Omegalodon
- Omerta: City of Gangsters
- OmniBus
- On Rusty Trails
- On the Front Line
- On the Road: Truck Simulator
- One Lonely Outpost
- One More Dungeon
- One More Gate: A Wakfu Legend
- One Ship, Two Ship, Redshift Blueshift
- One Step from Eden
- Open Fire Gold
- Operation Stormfront
- OPUS: Echo of Starsong
- Opus Magnum
- OPUS: Rocket of Whispers
- Orbital Gear
- Orczz
- Order of Battle: Blitzkrieg
- Order of Battle: Burma Road
- Order of Battle: Endsieg
- Order of Battle: Kriegsmarine
- Order of Battle: Morning Sun
- Order of Battle: Pacific
- Order of Battle: Panzerkrieg
- Order of Battle: Red Star
- Order of Battle: Red Steel
- Order of Battle: Red Storm
- Order of Battle: Rising Sun
- Order of Battle: Sandstorm
- Order of Battle: U.S. Marines
- Order of Battle: U.S. Pacific
- Order of Battle: Winter War
- Orion: A Sci-Fi Visual Novel
- Orion Trail
- Orphan
- Orwell: Ignorance Is Strength
- Orwell: Keeping an Eye on You
- Orwell's Animal Farm
- Oscura: Lost Light
- Oscura: Second Shadow
- Osmos
- Ossuary
- Ostrich Island
- Osy Osmosis
- Other 99, The
- Otokiyome
- OTTTD
- Out of Reach
- Out of Space
- Out of the Park Baseball 10
- Out of the Park Baseball 11
- Out of the Park Baseball 12
- Out of the Park Baseball 16
- Out of the Park Baseball 17
- Out of the Park Baseball 23
- Out of the Park Baseball 25
- Out There
- Out There Somewhere
- Outbreak: The New Nightmare
- Outbreak: The Nightmare Chronicles
- Outlast
- Outlast: Whistleblower
- Outpost 13
- Outracer
- Outreach
- Over the Alps
- Overboard!
- Overcooked! 2
- Overfall
- Overgrowth
- Overland
- Overload
- Overruled!
- Ovivo
- Owlboy
- Oxenfree 2: Lost Signals