PC - O
- O.D.T.
- O.D.T. Escape - Or Die Trying
- O.R.B.
- O.R.B. - Off-World Resource Base
- O.R.B. Off World Resource Base
- O2 Jam Bot
- O2Jam NX
- Oasis
- Oasis v1.0
- Oath (The)
- Obama - Presidential Escape
- Obama Potter and the Magic Coin
- Obama Saw Game
- Oben
- Oberon Media LEGO Fever v1.0
- Obitus
- Oblitus
- Oblivion
- Oblivion - Shivering Isles
- Oblivious Garden - Carmina Burana
- Obludia
- Obscura - the Shadow Blade
- Obscure
- Obscure - Learn About Fear
- Obscure - the Aftermath
- Obscure 2
- Obscure 2 Collection
- Obscure Collection
- Obsidian
- Obulis
- Ocean Battle
- Ocean Commander
- Ocean Trader
- Ocean Trader = Der Reeder
- OceanDive
- Oceanhorn - Monster of Uncharted Seas
- Oceanhorn Monster of Uncharted Seas
- Oceanhorn Monster of Uncharted Seas V1.03
- ocracy
- ocracy - Im Namen von Quetzalcoatl
- ocrazy
- Octodad - Dadliest Catch
- Odallus - the Dark Call
- OddBallz
- Oddworld - Abes Exoddus
- Oddworld - Abes Oddysee
- Oddworld - Abe's Exoddus
- Oddworld - Abe's Exodus
- Oddworld - Abe's Oddysee
- Oddworld - Abe's Oddysee - New 'n' Tasty
- Oddworld - Abes Exodus
- Oddworld - Abes Odyssey
- Oddworld - Munch's Oddysee
- Oddworld - New 'n' Tasty!
- Oddworld - New 'n' Tasty! v1.0
- Oddworld - Stranger's Wrath
- Oddworld - Stranger's Wrath HD
- Oddworld - Strangers Vergeltung
- Oddworld 2
- Oddworld 2 - Abe's Exoddus
- Oddworld 2 - Abe's Exxodus
- Oddworld New n Tasty
- Odell Down Under
- Odieus' Quest for the Magic Fling-Shot
- Odieus's Quest for the Magic Fling-Shot
- Odium
- ODT
- Odyssee - Auf der Suche nach Odysseus
- Odyssey
- Odyssey - the Search for Ulysses
- Of Light & Darkness
- Of Light and Darkness
- Of Light and Darkness - the Prophecy
- Of Orcs and Men
- Off-Road Drive
- Off-Road Redneck Racing
- Off-Road Velociraptor Safari
- Offensive
- Office
- Office Escape
- Office Escape - Stage 3
- Officers
- Official Formula 1 Racing
- Official Hamster Republic RPG Creation Engine
- Official Team Manager
- Offroad
- Offspring Fling
- Offworld Trading Company
- Offworld Trading Company v0.5.7567
- Offworld Trading Company V0.6.8172
- Offworld Trading Company version 0.2.5792
- OGame
- Oh no! More Lemmings
- Oh no! More Lemmings!
- Oh! Pai
- OH! RPG!
- Oil Enterprise
- Oil Imperium
- Oil Rush
- Oil Tycoon
- Oil Tycoon 2
- Oil's Well
- OK! Puzzle Stars
- Oknytt
- Old Empire
- Oldtimer
- OlliOlli
- Olympic Games
- Omar Sharif Bridge 2
- Omar Shariff Bridge 2
- Omega Stone
- Omerta - City of Gangsters
- Omerta City of Gangsters Gold GOG
- Ometa City of Gangsters V1.07
- OMG Zombies v1.00
- OMG Zombies!
- Omicron - the Nomad Soul
- Omikron
- Omikron - the Nomad Soul
- Omnicron Conspiracy
- Omnom Forest
- On My Own
- On the Ball, League Edition
- Once Bitten, Twice Dead
- Once Upon A Knight
- Once Upon A Knight (Knightshift)
- One Finger Death Punch
- One Finger Death Punch Steam
- One Manga Day
- One More Dungeon
- One More Dungeon V1.0.3
- One Must Fall
- One Must Fall - 2097
- One Must Fall - Battlegrounds
- One Must Fall 2097
- One Piece - Grand Battle
- One Piece - Grand Battle 3
- One Piece - Pirate Warriors 3
- One Piece Pirate Warriors 3
- One Step Beyond
- One Unit Whole Blood
- One Way Heroics
- One Way Heroics Plus
- One Way To Die
- onEscapee
- Onesimus - A Quest for Freedom
- Oni
- Oni (Savegame Editor)
- Oniblade
- Oniken
- Onikira - Demon Killer
- Onikira Demon Killer V1.739
- Onimusha
- Onimusha - Warlords
- Onimusha 3
- Onimusha 3 - Demon Siege
- Only If
- Onslaught
- Ooops Up
- Oozi - Earth Adventure
- Open Doors 2
- Open Kart
- Open Season
- Opening Weekend - Big Cats Season
- Opening Weekend - Deer Season
- Opening Weekend - Varmint Season
- OpenIt
- OpenIT v2.2
- OpenIt v2.62
- OpenTTD
- Opera Fatal
- Operation - Inner Space
- Operation - Matriarchy
- Operation - Sea Storm
- Operation Air Assault
- Operation Air Assault 2
- Operation BlackSquare
- Operation Blitzsturm
- Operation Blockade
- Operation Body Count
- Operation Carnage
- Operation Crusader
- Operation Desert Hammer
- Operation Flashpoint
- Operation Flashpoint - Cold War Crisis
- Operation Flashpoint - Dragon Rising
- Operation Flashpoint - Red Hammer
- Operation Flashpoint - Red Hammer + Resistance
- Operation Flashpoint - Red River
- Operation Flashpoint - Resistance
- Operation Flashpoint - Resistance v1.75
- Operation Flashpoint - Resistance v1.85
- Operation Flashpoint - US v1.40
- Operation Flashpoint 2 - Dragon Rising
- Operation Flashpoint Demo
- Operation Flashpoint Red River Steam
- Operation Flashpoint Resistance v1.90
- Operation Flashpoint Resistance v1.91
- Operation Flashpoint v1.20
- Operation Flashpoint v1.46
- Operation Flashpoint v1.55 MP TEST
- Operation Mania
- Operation Meteorit
- Operation Meteorite
- Operation Meteoroid
- Operation Rail
- Operation Spacehog
- Operation Stealth
- Operation Thunderbolt
- Operation Thunderstorm
- Operation Tiger Hunt
- Operation Victory
- Operation Wolf
- Operation Wolfsburg
- Operational Art of War 1
- Operational Art of War 2
- Operative - No One Lives Forever
- Oplossing Eggerland 3
- Opplosing Eggerland
- Opplossing Eggerland 3
- Options-Experte
- Orange Box
- ORB
- Orbital Gear
- Orbitalis
- Orbs of Attrition
- Orbs of Attrition v1.05
- Orc Attack - Flatulent Rebellion
- Orc Attack - Flatulent Rebellion v1.0
- Orchestrated Death
- Orcs Must Die
- Orcs Must Die 2
- Orcs Must Die 2 (v1.0.0.264)
- Orcs Must Die 2 (v1.0.0.294)
- Orcs Must Die 2 (v1.0.0.316)
- Orcs Must Die 2 V1.0.0.362 Steam
- Orcs Must Die!
- Orcs Must Die! 2
- Orczz
- Order - 1886
- Order of Battle - Pacific
- Order of War
- Order of War V1.0.2423 DX10
- Oregon Trail
- Oregon Trail - 5th Edition
- Oregon Trail 2
- Oregon Trail 3
- Oregon Trail 3 Anniversary
- Organ Trail - Director's Cut
- Organic Panic - Early Access
- Ori and the Blind Forest
- Ori and the Blind Forest v1.0
- Ori and the Blind Forest V1.12.2016
- Origamo
- Origin of the Species
- Original War
- Original War v1.02/1.05
- Orion - Dino Beatdown
- ORION - Dino Horde
- Orion - Prelude
- Orion Burger
- Orion Conspiracy
- ORION Prelude
- Orion Trail
- Oscar
- Oscura - Lost Light
- Osiris
- Osmos
- Ostfront
- Ostrich Island
- Ostrich Runner
- Other Dimension
- Other Dimension The
- Otomaco
- Otto Matic
- OTTTD
- Ougon Musou Kyoku
- Ougon Musou Kyoku Cross
- Our Darker Purpose
- Our Love Will Grow V1.1
- OurWorld
- Out from Room
- Out of the Park 3
- Out of the Park Baseball 15
- Out of the Park Baseball 16
- Out of the Park Baseball 3
- Out of This World
- Out There - Omega Edition
- Out There Omega version 1.1.2
- Out There Somewhere
- Out To Lunch
- Outbound
- Outbreak
- OutBreak v1.0
- Outbreak v1.3
- Outbreak v1.7
- Outbreak v1.8
- Outbreak v1.81
- Outbreak v1.82
- Outbreak v1.85
- Outbreak v1.9
- Outbreakers
- Outcast
- Outcome
- Outdoor Life - Sportsman's Challenge
- Outdoor Life Sportsman's Challenge
- Outdoor Life Sportsmans Challenge
- Outer Ridge
- Outer Ridge (Reg. Version)
- Outforce
- Outland
- Outland v113
- Outlast
- Outlast - Whistleblower
- Outlast Whistleblower V1.0.12046
- Outlaw Chopper
- Outlaw Golf
- Outlaw Golf 2
- Outlaw Racers
- Outlaws
- Outliner
- Outliner v1.02
- Outlive
- Outpost
- Outpost 1
- Outpost 2
- Outpost 2 - Divided Destiny
- Outpost 2 Divided Destiny
- Outpost Kaloki
- Outrage
- Outrage +2 Trainer
- Outrun
- OutRun 2006
- Outrun 2006 - Coast 2 Coast
- OutRun 2006 - Coast to Coast
- Outwars
- Oval Office
- Over 9,000 Zombies!
- Over 9000 zombies!
- Over the Hedge
- Over the Reich
- Overboard
- Overboard!
- Overclocked
- Overclocked - A History of Violence
- Overdrive
- Overkill
- Overload
- Overlord
- Overlord - Fellowship of Evil
- Overlord - Raising Hell
- Overlord (1990)
- Overlord (2001)
- Overlord (2007)
- Overlord 2
- Overlord 2 V1
- Overlord 2007
- Overlord Fellowship of Evil V1.00
- Overlord v1.0
- Overlord v1.01b
- Overlord v1.2
- Overruled!
- Overseer
- OverTower v1.7
- Overture
- Overwatch
- Oxid
- Oxyd
- Oxyd Extra
- Oxyd Magnum
- Oyaji no Himatsubushi - Shanghai Dragon's Eye
- Oyaji no Himatsubushi - Shanghai Dragon's Eye
- Oyakusoku Love
- Oyomesan wa Hime Fujo