| Oriental Blue: Ao no Tengai (2003) | 67,565 | 117 |
| Oriental Empires (2016) | 3,165,425 | 1,058 |
| Oriental Games (1990) | 876 | 13 |
| Oriental Valley (2024) | 46,334 | 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) | 2,146,789 | 2,298 |
| The Original Wizard (2023) | 85,877 | 24 |
| Orion (1983) | 6,749,162 | 40 |
| Orion Burger (1996) | 138,877 | 110 |
| The Orion Conspiracy (1995) | 85,860 | 67 |
| Orion: A Sci-Fi Visual Novel (2015) | 5,494 | 19 |
| ORION: Dino Beatdown (2012) | 4,269,009 | 166 |
| Orion: Prelude (2012) | 6,096,765 | 1,382 |
| Orion: The Eternal Punishment (2021) | 909 | 2 |
| Ork (1991) | 4,297,654 | 249 |
| ORKANA CONFLICT VR (2021) | 13,487 | 26 |
| Orly's Draw-A-Story (1997) | 39,733 | 11 |
| Ornament Express (2023) | 169 | 8 |
| Orphan (2018) | 15,364,861 | 683 |
| Orphan Age (2020) | 10,210,276 | 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) | 705,071 | 581 |
| The ORPHEUS Ruse (2015) | 602 | 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) | 128,407 | 207 |
| Ortharion : The Last Battle (2023) | 15,767 | 101 |
| Orwell (2016) | 1,234,521 | 1,034 |
| Orwell's Animal Farm (2020) | 210,848 | 134 |
| Orwell: Ignorance is Strength (2018) | 353,384 | 334 |
| Orwell: Keeping an Eye On You (2016) | 938,445 | 917 |
| ORX (2022) | 3,082,294 | 653 |
| Oryks (2024) | 0 | 0 |
| Oscar (1993) | 414,952 | 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) | 122,185 | 114 |
| Osiris: New Dawn (2016) | 48,520,127 | 10,964 |
| Osman (1996) | 451,674,709 | 3,772 |
| Osmos (2009) | 63,057,591 | 701 |
| OSR Unhinged (2010) | 0 | 0 |
| Ossuary (2015) | 22,673 | 49 |
| Ostalgie: The Berlin Wall (2018) | 416,954 | 301 |
| Osteoblasts (2021) | 39,153 | 130 |
| Ostranauts (2020) | 3,208,919 | 1,602 |
| Ostrich Island: Escape from Paradise (2015) | 6,253,799 | 87 |
| Ostrich Runner (2004) | 42,551 | 107 |
| Ostriv (2020) | 28,319,187 | 8,219 |
| Ostrom (2024) | 116,057,725 | 15 |
| Ostron (1983) | 151 | 2 |
| osu! (2007) | 1,635,696,394 | 223,045 |
| Osu! Tatakae! Ouendan (2005) | 618,797 | 180 |
| 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) | 61,285,028 | 2,098 |
| Otem's Defiance (2016) | 18,521 | 41 |
| Othello (1980) | 12,357 | 18 |
| Othello (1986) | 77,216 | 175 |
