O
- O.W.S.P
- Observer
- Observer 2
- Observer Redux
- Obsidian Conflict
- Obversion
- Occult-Scrim
- Oculus
- Oddworld: Fangus
- Oddworld: Stranger's Wrath
- Ode to a moon
- Offensive Combat
- Omega Point
- On Air
- Once Bitten Twice Dead
- Once Upon a Time in Roswell
- Onslaught
- Onward
- OpenArena
- Operation 7
- Operation: Black Mesa
- Operation: Downtown Destruction
- Operation: Gral
- Operation: Harsh Doorstop
- Operation: Matriarchy
- Operation: Take-Down
- Operation: Tango
- Operation COVID-19
- Operation Flashpoint
- Operation Flashpoint: Dragon Rising
- Operation Flashpoint: Red River
- Operator8
- Opposing-Force
- ORANGEfps
- Origin
- Origin Access Basic
- Origin Access Premier
- Orion13
- Orion: Dino Beatdown
- ORION: Instincts
- Orion: Prelude
- Orion Project
- Outbreak Island
- Outbreak Island: Pendulum
- Outbreak New Dawn
- Outer Wilds
- Outlast
- Outlast 2
- Outlaws
- Outlaws of the Old West
- OUTLIER
- Out of Action
- Outpost: Infinity Siege
- Outpost Zero
- Outreach
- Outriders
- Outrise
- Overcast - Walden and the Werewolf
- Overcooked 2
- OVERGUN
- Overkill
- Overkill's The Walking Dead
- Overkill VR
- overlay
- Overload
- Overwatch
- Overwatch 2
- OVERWHELM
- Oxide Room 104