| One Dove Above | Developer | |
| One Fox | Developer | |
| One Gruel Studio | Developer | |
| One Guy Games | Developer | |
| One Guy Studio | Developer | |
| One Hand Free Studios | Developer | |
| One Happy Giant | Developer | |
| One Hit Combo Studio | Developer | |
| One Man Army FL | Developer | |
| One More Dream Studios | Developer | |
| One More Level | Developer | |
| One True Game Studios | Developer | |
| One Up Plus Entertainment | Developer | |
| One Week Productions (Colin Swinbourne, Kevin Parker, Martin Severn, Andrew Severn, Mike Brown) | Developer | |
| One Week Productions (Kevin Parker, Colin Swinbourne, Martin Severn, Andrew Severn) | Developer | |
| One Week Productions (Kevin Parker, Colin Swinbourne, Martin Severn, Andrew Severn, Mike Brown) | Developer | |
| One Week Productions (Kevin Parker, Martin Severn) | Developer | |
| One Wolf | Developer | |
| One or Eight | DeveloperPublisher | |
| One-bit Punch | Developer | |
| OneDollar | Developer | |
| OneEgg42 | Developer | |
| OneGameDad | Developer | |
| OneGuyGames | Developer | |
| OneHundredThousand | Developer | |
| OneManArmy | Developer | |
| OneManArmyStudios | Developer | |
| OneManBand | Developer | |
| OneMoreLevel | Developer | |
| OneNine Studios | Developer | |
| OnePieceOnlineRPG | Developer | |
| OnePixelMonster | Developer | |
| OneSecretPseudo | Developer | |
| OneShark | Developer | |
| OneThatEatYou | Developer | |
| OneZeroDev | Developer | |
| Onebraverobot | Developer | |
| OneginIII | Developer | |
| Oneiric Worlds | Developer | |
| Oneirocritica Games | Developer | |
| Oneiromancer | Developer | |
| OneorEight | Developer | |
| Onerat Games | Developer | |
| OneratGames | Developer | |
| Onesong Partners | Developer | |
| Onevision | DeveloperPublisher | |
| Onevision Games | DeveloperPublisher | |
| Ongakukan | DeveloperPublisher | |
| OnheXon Entertainment | Developer | |
| Oni Elite | Developer | |