| Omen Exitio: Hunger (2024) | 514 | 11 |
| Omen Exitio: Plague (2018) | 43,069 | 184 |
| Omen of Sorrow (2018) | 2,266,790 | 1,669 |
| Omensight (2018) | 1,013,262 | 2,086 |
| Omerta: City of Gangsters (2013) | 3,507,452 | 2,028 |
| Ometron (1983) | 265 | 1 |
| OMFG: One Million Fatal Guns (2021) | 17,170 | 136 |
| OMG Words (2025) | 17,371 | 13 |
| OMG! Not Another Isekai (2023) | 0 | 0 |
| OMG-Z (2011) | 46,817 | 52 |
| Omi Oh My AI (2022) | 1,272 | 11 |
| Omikron: The Nomad Soul (1999) | 12,428,651 | 1,693 |
| Ominoflux (2024) | 0 | 0 |
| Ominous Horizons: A Paladin's Calling (2001) | 15,357 | 20 |
| Ominous Objects: Family Portrait (2014) | 28,785 | 69 |
| Ominous Objects: Lumina Camera (2016) | 11,998 | 78 |
| Ominous Objects: Phantom Reflection (2015) | 48,796 | 91 |
| Ominous Objects: The Cursed Guards (2017) | 23,769 | 45 |
| Ominous Objects: Trail of Time (2015) | 32,867 | 44 |
| Ominous Stew (2025) | 0 | 0 |
| Ominous Tales: The Forsaken Isle (2017) | 9,914 | 55 |
| Omni Axes (2023) | 0 | 1 |
| Omnibion War (2020) | 21,311 | 32 |
| Omniblast (2021) | 0 | 1 |
| Omnibullet (2023) | 21,979 | 7 |
| OmniBus (2016) | 23,193,294 | 1,088 |
| Omnicube (2018) | 2,605 | 6 |
| OmniFootman (2019) | 66,244 | 49 |
| Omnigon (2023) | 2,393 | 1 |
| Omnimancer (2024) | 1 | 1 |
| OMNIMUS (2019) | 3,898 | 21 |
| Omnipresent (2015) | 115,965 | 12 |
| Omno (2021) | 4,788,872 | 5,709 |
| Omoide ni Kawaru Kimi (2002) | 1,308 | 10 |
| Omori (2020) | 305,137,151 | 64,003 |
| OMSI 2 (2013) | 245,917,961 | 72,154 |
| OMSI: The Bus Simulator (2011) | 98,188,238 | 8,783 |
| Omurice Next Time (2024) | 118 | 4 |
| OMUSUBI (2024) | 125,396 | 58 |
| On a Roll (2017) | 3,596,611 | 390 |
| On A Roll 3D (2015) | 2,802 | 21 |
| On a Summer Night (2025) | 5 | 2 |
| On Air (2021) | 116,779,647 | 3,525 |
| On Dark Terms (2023) | 98,416 | 53 |
| On My Own (2016) | 184,895,587 | 1,866 |
| On my own: A Hot Isekai Adventure (2023) | 0 | 0 |
| On Point (2024) | 9,836,411 | 758 |
| On Reflection (2007) | 117,987 | 10 |
| On Rusty Trails (2016) | 66,505 | 74 |
| On the Ball (1993) | 6,717,209 | 508 |
| On the Dragon Wings - Birth of a Hero (2022) | 1,047 | 7 |
| On the Hunt (2024) | 878,597 | 444 |
| On The Job (2023) | 3,776,288 | 360 |
| On the Peril of Parrots (2023) | 605 | 6 |
| On The Road: Truck Simulator (2017) | 6,892,025 | 2,700 |
| On the Run: Rogue Heroes (2024) | 801 | 1 |
| On The Wind's Breath (2025) | 0 | 0 |
| On Your Hands (2022) | 242,144 | 34 |
| On Your Tail (2024) | 1,231,800 | 366 |
| On-Court Tennis (1984) | 14,639 | 14 |
| Once a Pawn a King (2025) | 0 | 0 |
| Once a Porn a Time 2 (2024) | 0 | 0 |
| Once a Porn a Time: Porn and Cards (2025) | 0 | 0 |
| Once a Tale (2024) | 12,073 | 56 |
| Once Again (2022) | 33,720,948 | 3,010 |
| Once Alive (2024) | 12 | 1 |
| Once Bitten, Twice Dead! (2015) | 162,842 | 35 |
| Once Human (2024) | 128,360,676 | 45,529 |
| Once on a windswept night (2017) | 1,453 | 34 |
| Once Up (2025) | 0 | 0 |
| Once upon a Dungeon - Infinity (2025) | 3,633 | 18 |
| Once upon a Dungeon II (2023) | 944 | 10 |
| Once Upon a Jester (2022) | 293,460 | 309 |
| Once Upon A KATAMARI (2025) | 673 | 12 |
| Once Upon A Puppet (2025) | 265,933 | 369 |
