| Odyssey: The Deep Space Expedition (2019) | 328 | 1 |
| Odyssey: The Search for Ulysses (2000) | 23,454 | 31 |
| Oedipus Dating Sim (2018) | 34 | 1 |
| Oedipus/Antigone (2024) | 0 | 0 |
| Of Bird and Cage (2021) | 287,098 | 429 |
| Of Blades & Tails (2022) | 435,387 | 289 |
| Of Gods and Men: The Daybreak Empire (2018) | 6,398 | 18 |
| Of Guards And Thieves (2014) | 1,250,899 | 350 |
| Of Kings and Men (2016) | 3,345,430 | 285 |
| Of Lies and Rain (2025) | 158,421 | 93 |
| Of Light and Darkness: The Prophecy (1998) | 5,975 | 10 |
| Of Love And Sorrow (2016) | 58 | 1 |
| OF MICE AND SAND -REVISED (2018) | 17,578 | 115 |
| Of Mice and Sand: Revised (2017) | 33,572 | 88 |
| Of Orcs and Men (2012) | 6,167,948 | 2,913 |
| of pawns & kings (2023) | 936 | 5 |
| Of Ships & Scoundrels (2019) | 21,355 | 26 |
| Off (2008) | 3,801,664 | 1,267 |
| Off Course ELEMENTS of SPACE (2024) | 6 | 2 |
| Off Road (2008) | 606,337,010 | 29,113 |
| Off Road Challenge (1997) | 3,365,865 | 496 |
| Off Shore Warrior (1988) | 11,179 | 16 |
| Off The Record: Liberty Stone (2015) | 44,843 | 62 |
| Off The Record: The Art of Deception (2015) | 46,642 | 78 |
| Off the Record: The Final Interview (2015) | 32,486 | 57 |
| Off the Record: The Italian Affair (2014) | 44,538 | 100 |
| Off the Record: The Linden Shades (2013) | 28,986 | 43 |
| Off The Road Unleashed (2021) | 13,368,192 | 1,298 |
| Off the Wall (1991) | 1,536,827 | 211 |
| Off-Road Drive (2011) | 22,499,210 | 1,901 |
| Off-Road Paradise: Trial 4x4 (2017) | 627,824 | 53 |
| Off-Road Redneck Racing (2001) | 35,059 | 40 |
| Off-Road Super Racing (2016) | 194,287 | 39 |
| Off-Road Velociraptor Safari (2008) | 35,980 | 19 |
| Off-World Interceptor (1994) | 115,407 | 217 |
| Offendron Warrior (2018) | 130 | 6 |
| Offensive Combat (2017) | 1,010,792 | 271 |
| Offensive Dimensions (2017) | 23 | 1 |
| OFFERING APP (2023) | 6,388 | 5 |
| Office After Hours (2025) | 722,520 | 93 |
| Office Battle (2015) | 23,789,024 | 114 |
| Office Disorders (2010) | 205 | 2 |
| Office Fight (2024) | 53,365 | 55 |
| Office Girls and Games (2023) | 303 | 6 |
| Office Management 101 (2022) | 68,345 | 61 |
| Office Nightmare Chapter 1 Alpha (2024) | 167 | 1 |
| Office Overloaded (2025) | 42 | 1 |
| The Office Quest (2018) | 13,332,956 | 648 |
| Office Run (2022) | 906 | 26 |
| Office Simulator (2020) | 0 | 0 |
| The Office Type (2025) | 94 | 5 |
| Officers (2008) | 1,209,470 | 204 |
| Official Formula One Racing (1999) | 15,357 | 28 |
| OffRoad Drive Desert (2016) | 25,975,239 | 1,193 |
| Offroad Driving Simulator 4x4 (2017) | 1,748,809 | 113 |
| Offroad Legends (2012) | 1,830,202 | 301 |
| Offroad Legends 2 (2014) | 3,004,750 | 862 |
| Offroad Mini Racing (2021) | 26,333 | 6 |
| Offroad Racing (2019) | 1,588,832 | 628 |
| Offroad Thunder (1999) | 72,567 | 90 |
| Offroad Track Simulator 4x4 (2015) | 9,457 | 12 |
| Offroad Truck Racing (2022) | 36,655 | 16 |
| Offroad: Dead Planet (2023) | 275 | 8 |
| Offside (2022) | 11,710,732 | 249 |
| Offspring Fling (2012) | 867,949 | 206 |
| Offworld Trading Company (2016) | 9,541,575 | 3,163 |
| Oftalmogarden (2021) | 0 | 0 |
| OG Puzzlers: Synthwave Astronauts (2024) | 0 | 0 |
| OG Puzzlers: Synthwave Dinosaurs (2024) | 8 | 2 |
| OG Puzzlers: Synthwave Knights (2024) | 0 | 1 |
| OG Puzzlers: Synthwave Monsters (2024) | 0 | 1 |
| OGame (2002) | 15,154,662 | 1,395 |
| Ogre (1986) | 13,262 | 44 |
| Ogre Battle 64: Person of Lordly Caliber (1999) | 2,892,581 | 2,662 |
| Ogre Battle Gaiden: Prince of Zenobia (2000) | 5,597 | 5 |
