| Orange | DeveloperPublisher | |
| Orange Flag | Developer | |
| Orange Games | Developer | |
| Orange House | DeveloperPublisher | |
| Orange Juice Dog | Publisher | |
| Orange One | Developer | |
| Orange Pixel | DeveloperPublisher | |
| Orange Pylon | Developer | |
| OrangeeZ | Developer | |
| Orangepixel | DeveloperPublisher | |
| Orator | Developer | |
| Oraylien | Developer | |
| Orb | Developer | |
| Orbit Studio | Developer | |
| Orbital Media | Developer | |
| Orbital Media, Inc. | DeveloperPublisher | |
| Orbital Speed Studio | DeveloperPublisher | |
| OrbitalNine | Developer | |
| OrbitalShark | Developer | |
| OrbitalWorks | Developer | |
| Orblus | Developer | |
| Orc Wizard | Developer | |
| Orca | Publisher | |
| Orcalancelulu | Developer | |
| Orchid Games | Developer | |
| Orcolom | Developer | |
| Ordilogic Systems | Developer | |
| Oreganik | Developer | |
| Oregin | Developer | |
| Oren Erlich | Developer | |
| Orenda | Publisher | |
| Orenge | Developer | |
| Orenge Crest | Developer | |
| Orenji_games | Developer | |
| Orenki | Developer | |
| Oreolek | Developer | |
| Oretal | Developer | |
| Orfeas Game Studio | Developer | |
| OrfeasWorldGames Studio | Developer | |
| OrgAction Games | Developer | |
| Organa | Developer | |
| Ori Brusilovsky | Developer | |
| Oriental | Publisher | |
| Oriental Soft | Publisher | |
| Origame Digital | Developer | |
| Origin | Publisher | |
| Origin Systems | DeveloperPublisher | |
| Original Fire Games | Developer | |
| Original Gamer Stevie Strow | Developer | |
| OriginalFei | Developer | |
| 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 | |
| OsmineeNitro | Developer | |
| Osmodium | Developer | |
| Osogato | Developer | |
| Osome Studio | DeveloperPublisher | |
| Ossete Games | Developer | |
| Ossian Studios | Developer | |
| Osspial | Developer | |
| Ostmark | Developer | |
| Ostrich Banditos | Developer | |
| Ostrze | Developer | |
| Otaara | Developer | |
| Otaboo | Developer | |
| Otadanku Productions | Developer | |
| Otaku Publishing Ltd. | Publisher | |
| OtakuHeroSama | Developer | |
| OtakuNerdGirl | Developer | |
| OtasGamer64 | Developer | |
| OtavioPastore | Developer | |
| Otay | Developer | |
| Otham | Developer | |
| Othelbark | Developer | |
| Other Ocean | DeveloperPublisher | |
| Other Ocean Interactive | DeveloperPublisher | |
| Other Tales Interactive | Developer | |
| Otherside Bay | Developer | |
| Otherside Entertainment | Developer | |
| Otherside Games | Developer | |
| OtherwiseAPPs | Developer | |
| OtisDev | Developer | |
| Otomate | Developer | |
| Otome Palace | Developer | |
| Otori Denshi | Developer | |
| Otozip | Developer | |
| Otsirave | Developer | |
| OtspIII | Developer | |
| Ottara Studio | Developer | |
| OtterWays | Developer | |
| Otterqueen | Developer | |
| Ouch Giver Games | Developer | |
| Ouch Mouse Studio | Developer | |
| OuchyBiteGuy | Developer | |
| Oudidon | Developer | |
| OuickTequila | Developer | |
| Ouili | Developer | |
| Ouji Akamine | Developer | |
| Oulsen | Developer | |
| Our Land Team | Developer | |
| Our Little Studio | Developer | |
| Ouro | Developer | |
| Ouro Eight | Developer | |
| OursBleu | Developer | |
| Ourson | Developer | |
| Out Of The Loop | Developer | |
| Out Of Tune Games | Developer | |
| Out of Box Games | Developer | |
| Out of Phayze | Developer | |
| Out of the Blue | Developer | |
| Out of the Park Developments | DeveloperPublisher | |
| OutLook Entertainment | Developer | |
| OutOfDate | Developer | |
| OutOut | Developer | |
| OutSide Directors Company | Developer | |
| Outback | Developer | |
| Outdoor Partners | Developer | |
| Outer Clouds Games | Developer | |
| OuterCloudStudio | Developer | |
| OuterRimStudios | Developer | |
| Outerlight | Developer | |
| Outerminds Alpha | Developer | |
| Outerminds Omega | Developer | |
| OutermostDev | Developer | |
| Outflank Strategy Wargames | Developer | |
| Outfrost | Developer | |
| Outgunned Games | Developer | |
| Outlander Games | Developer | |
| Outlands | Developer | |
| Outlaw Software | Developer | |
| Outlaws Studio | Developer | |
| Outlook Entertainment | Developer | |
| Output Games | Developer | |
| Outrage Entertainment | Developer | |
| Outrage Games | Developer | |
| Outrigger Koubou | Publisher | |
| Outright Games | DeveloperPublisher | |
| Outsider Games | DeveloperPublisher | |
| Outsider Team | Developer | |
| Outspark | Publisher | |
| OutspokenWalnut Studios | Developer | |
| OveAhlman | Developer | |
| OveR-Software | Developer | |
| Over Cooked Code Games | Developer | |
| Over Fence | Developer | |
| Over The Top Games | Developer | |
| Over the Moon | DeveloperPublisher | |
| Over the Rainbow Studios | Developer | |
| Over the Top Games | Developer | |
| Over-9000 | Developer | |
| OverGamez | DeveloperPublisher | |
| OverPowered Team | Developer | |
| OverTune | Developer | |