| Orgynizer (2022) | 16,394 | 17 |
| Ori and the Blind Forest (2015) | 248,674,361 | 98,976 |
| Ori and the Will of the Wisps (2020) | 108,344,317 | 69,325 |
| Oriental Blue: Ao no Tengai (2003) | 67,566 | 117 |
| Oriental Empires (2016) | 3,165,695 | 1,058 |
| Oriental Games (1990) | 876 | 13 |
| Oriental Valley (2024) | 46,343 | 35 |
| Origami Flight (2019) | 705 | 7 |
| Origami Lovers (2023) | 522 | 10 |
| Origami Treasure (2024) | 89 | 3 |
| Origin Of Destiny: Crimson Awakening (2016) | 144 | 2 |
| Original War (2001) | 2,155,069 | 2,325 |
| The Original Wizard (2023) | 0 | 0 |
| Orion (1983) | 6,749,162 | 40 |
| Orion Burger (1996) | 138,877 | 110 |
| The Orion Conspiracy (1995) | 85,909 | 67 |
| Orion: A Sci-Fi Visual Novel (2015) | 5,494 | 19 |
| ORION: Dino Beatdown (2012) | 4,269,009 | 166 |
| Orion: Prelude (2012) | 6,096,813 | 1,382 |
| Orion: The Eternal Punishment (2021) | 909 | 2 |
| Ork (1991) | 4,297,838 | 251 |
| ORKANA CONFLICT VR (2021) | 13,487 | 26 |
| Orly's Draw-A-Story (1997) | 39,791 | 13 |
| Ornament Express (2023) | 169 | 8 |
| Orphan (2018) | 15,368,605 | 685 |
| Orphan Age (2020) | 10,210,279 | 490 |
| Orphan Black: The Game (2017) | 7,334,417 | 20 |
| The Orphan Dreams (2016) | 147,799 | 22 |
| Orphan of the Petal (2019) | 15 | 1 |
| The Orphan: A Pop-Up Book Adventure (2023) | 426 | 10 |
| Orphen: Scion of Sorcery (2000) | 706,310 | 584 |
| The ORPHEUS Ruse (2015) | 604 | 3 |
| Orpheus's Dream (2019) | 11,747 | 46 |
| Orpheus: Fall For Eurydice (2022) | 510 | 1 |
| Orpiment (2021) | 3,845 | 4 |
| ORR (2020) | 93,538 | 41 |
| Orrstead (2023) | 300,816 | 49 |
| Orten Was The Case (2023) | 128,412 | 207 |
| Ortharion : The Last Battle (2023) | 15,767 | 101 |
| Orwell (2016) | 1,234,693 | 1,046 |
| Orwell's Animal Farm (2020) | 217,981 | 135 |
| Orwell: Ignorance is Strength (2018) | 353,401 | 337 |
| Orwell: Keeping an Eye On You (2016) | 938,452 | 917 |
| ORX (2022) | 3,082,294 | 653 |
| Oryks (2024) | 0 | 0 |
| Oscar (1993) | 414,971 | 76 |
| Oscar der Ballonfahrer (2010) | 5,397 | 8 |
| Oscar's World Tour (2011) | 1,003 | 2 |
| OscarWildeCard (2023) | 1 | 1 |
| Oscuria - The world of nightmares (2021) | 566 | 5 |
| Oseong-gwa Haneum (1993) | 155 | 2 |
| OSES (2017) | 24 | 2 |
| OshiRabu: Waifus Over Husbandos (2020) | 122,192 | 114 |
| Osiris: New Dawn (2016) | 0 | 0 |
| Osman (1996) | 451,767,896 | 3,783 |
| Osmos (2009) | 63,059,485 | 705 |
| OSR Unhinged (2010) | 0 | 0 |
| Ossuary (2015) | 22,675 | 50 |
| Ostalgie: The Berlin Wall (2018) | 417,491 | 302 |
| Osteoblasts (2021) | 39,153 | 130 |
| Ostranauts (2020) | 3,532,553 | 1,757 |
| Ostrich Island: Escape from Paradise (2015) | 6,253,799 | 87 |
| Ostrich Runner (2004) | 42,706 | 108 |
| Ostriv (2020) | 28,337,665 | 8,265 |
| Ostrom (2024) | 116,057,725 | 15 |
| Ostron (1983) | 151 | 2 |
| osu! (2007) | 1,639,072,760 | 224,671 |
| Osu! Tatakae! Ouendan (2005) | 618,908 | 182 |
| Oswald's Adventure (2017) | 0 | 0 |
| Osyaberi! Horijyo! (2018) | 6,152 | 24 |
| Osyaberi! Puzzle Chigatan: Spot the Differences with Everyone (2020) | 2,016 | 4 |
| Otaku Engine (2022) | 233 | 1 |
| Otaku Miracles (2025) | 0 | 0 |
| Otaku no Seiza: An Adventure in the Otaku Galaxy (1991) | 407,357 | 130 |
| Otaku's Adventure (2019) | 61,993,435 | 2,144 |
