| Oretachi Game Center Zoku: Time Pilot (2005) | 650 | 2 |
| Organ Quarter (2017) | 339,180 | 371 |
| Organ Trail (2010) | 84,751 | 17 |
| Organ Trail (2011) | 9,545,590 | 2,400 |
| Organ Trail: Director's Cut (2013) | 1,719,687 | 423 |
| Organs Please (2021) | 2,136,262 | 646 |
| Orgarhythm (2012) | 203,599 | 56 |
| Orgynizer (2022) | 127 | 3 |
| Ori and the Blind Forest (2015) | 239,620,736 | 93,561 |
| Ori and the Will of the Wisps (2020) | 116,540,076 | 68,066 |
| Oriental Blue: Ao no Tengai (2003) | 64,777 | 105 |
| Oriental Empires (2016) | 4,792,272 | 1,239 |
| Oriental Games (1990) | 115,737 | 18 |
| Origin Of Destiny: Crimson Awakening (2016) | 125 | 2 |
| Original War (2001) | 2,050,633 | 2,208 |
| The Original Wizard (2023) | 85,396 | 22 |
| Orion (1983) | 7,827,504 | 111 |
| Orion Burger (1996) | 171,475 | 102 |
| The Orion Conspiracy (1995) | 75,466 | 61 |
| Orion: A Sci-Fi Visual Novel (2015) | 6,253 | 51 |
| ORION: Dino Beatdown (2012) | 3,540,920 | 112 |
| Orion: Prelude (2012) | 8,127,158 | 1,466 |
| Ork (1991) | 12,067,424 | 598 |
| ORKANA CONFLICT VR (2021) | 13,482 | 25 |
| Orly's Draw-A-Story (1997) | 50,314 | 9 |
| Ornament Express (2023) | 152 | 6 |
| Orphan (2018) | 10,109,928 | 1,071 |
| Orphan Age (2020) | 1,936,751 | 339 |
| Orphan Black: The Game (2017) | 13,565 | 19 |
| The Orphan Dreams (2016) | 144,822 | 19 |
| Orphan of the Petal (2019) | 15 | 1 |
| The Orphan: A Pop-Up Book Adventure (2023) | 431 | 10 |
| Orphen: Scion of Sorcery (2000) | 664,072 | 539 |
| The ORPHEUS Ruse (2015) | 529 | 3 |
| Orpheus's Dream (2019) | 3,835 | 43 |
| Orpheus: Fall For Eurydice (2022) | 756 | 2 |
| Orpiment (2021) | 6,376 | 3 |
| ORR (2020) | 2,755,060 | 224 |
| Orrstead (2023) | 181,863 | 46 |
| Ortharion : The Last Battle (2023) | 13,115 | 60 |
| Orwell (2016) | 1,872,106 | 1,277 |
| Orwell's Animal Farm (2020) | 180,476 | 118 |
| Orwell: Ignorance is Strength (2018) | 352,656 | 301 |
| Orwell: Keeping an Eye On You (2016) | 499,721 | 782 |
| ORX (2022) | 2,411,345 | 651 |
| Oscar (1993) | 1,529,346 | 111 |
| Oscar der Ballonfahrer (2010) | 0 | 0 |
| Oscar's World Tour (2011) | 1,003 | 2 |
| OscarWildeCard (2023) | 1 | 1 |
| Oscuria - The world of nightmares (2021) | 566 | 5 |
| Oseong-gwa Haneum (1993) | 90 | 1 |
| OSES (2017) | 66 | 3 |
| OshiRabu: Waifus Over Husbandos (2020) | 62,863 | 112 |
| Osiris: New Dawn (2016) | 48,858,860 | 10,984 |
| Osman (1996) | 447,782,611 | 5,216 |
| Osmos (2009) | 50,459,576 | 933 |
| OSR Unhinged (2010) | 6 | 1 |
| Ossuary (2015) | 19,675 | 36 |
| Ostalgie: The Berlin Wall (2018) | 322,614 | 269 |
| Osteoblasts (2021) | 37,747 | 124 |
| Ostranauts (2020) | 1,628,711 | 766 |
| Ostrich Island: Escape from Paradise (2015) | 6,295,045 | 93 |
| Ostrich Runner (2004) | 43,632 | 96 |
| Ostriv (2020) | 27,749,188 | 7,783 |
| Ostron (1983) | 159 | 2 |
| osu! (2007) | 1,554,330,176 | 223,196 |
| Osu! Tatakae! Ouendan (2005) | 612,508 | 178 |
| Osyaberi! Horijyo! (2018) | 5,357 | 19 |
| Osyaberi! Puzzle Chigatan: Spot the Differences with Everyone (2020) | 561 | 3 |
| Otaku Engine (2022) | 233 | 1 |
| Otaku no Seiza: An Adventure in the Otaku Galaxy (1991) | 411,255 | 140 |
| Otaku's Adventure (2019) | 58,409,628 | 2,120 |
| Otem's Defiance (2016) | 7,700 | 32 |
| Othello (1980) | 12,540 | 23 |
| Othello (1986) | 83,733 | 185 |
