| Noobow | Stardust Crusaders | Action > Platformer | GB | Fully Playable | 1.0 | 24 May 2018 | EN |
| Nushi Tsuri Adventure: Kite no Bouken | JaytheHam | Role Playing | GB | Fully Playable | 2.0 | 28 Aug 2018 | EN |
| Nyorols | PentarouZero | Action | MSX | Fully Playable | 1.00 | 02 Oct 2004 | EN |
| Ogre Battle: The March of the Black Queen | FinS | Strategy > Turn Based | SNES | Fully Playable | 1.2 | 11 Sep 2018 | EN |
| Oishinbo: Kyukyoku no Menu 3bon Syoubu | snark | Adventure | NES | Fully Playable | 1.0 | 15 May 2008 | EN |
| Ojou-sama no DokiDoki Daisakusen: Nowareta Ko no Kan | Mauve | Action > Platformer | PC | Fully Playable | 1.0 | 08 Apr 2012 | EN |
| Okaeri! Chibi-Robo! Happy Richie Oosouji | Cjuub | Action Adventure | NDS | Fully Playable | 1.1 | 13 Apr 2016 | EN |
| Okamoto Ayako to Match Play Golf: Ko Olina Golf Club in Hawaii | MrRichard999 | Sports | SNES | Fully Playable | 0.94 | 11 Dec 2015 | EN |
| Oni IV: Kishin no Ketsukozoku | Akujin | Role Playing | GB | Unfinished | 0.30 | 22 Feb 2000 | EN |
| Onyanko Town | pacnsacdave | Action | NES | Fully Playable | 1.0 | 17 Nov 2015 | EN |
| Ore ga Omae o Mamoru | Phantom | Action Adventure | NDS | Fully Playable | 1.0 | 07 Dec 2020 | EN |
| Ore no Imōto ga Konna ni Kawaii Wake ga Nai Portable ga Tsuzuku Wake ga Nai | Rinjinbu Translations | Visual Novel | PSP | Fully Playable | 1.0 | 31 Dec 2020 | EN |
| Oriental Blue: Ao no Tengai | Kingcom, Tom | Role Playing | GBA | Fully Playable | 1.0 | 16 Sep 2013 | EN |
| Otaku no Seiza: Adventure in the Otaku Galaxy | Suicidal Translations | Role Playing | NES | Unfinished | 0.0001cg | 28 Nov 2001 | EN |
| Otaku no Seiza: Adventure in the Otaku Galaxy | Stardust Crusaders | Role Playing | NES | Fully Playable | 1.01 | 09 Sep 2019 | EN |
| Otenba Becky no Daibouken | Sargon, hap | Action > Platformer | MSX | Fully Playable | 1.0 | 21 Jan 2010 | EN |
| Othello 2000 | Dark Tetsuya | Boardgame | GB | Unfinished | 0.001 | 22 Oct 2000 | EN |
| Otomedius | GameStone | Action > Shooter | ARC | Fully Playable | 1.0 | 12 May 2016 | EN |
| Otometeki Koi Kakumei Love Revo!! DS | jjjewel | Dating Sim | NDS | Fully Playable | 1.1 | 01 Jul 2012 | EN |
| Ottifanten - Kommando Stoertebeker | Matrix Arcade Division, Alemanic Translations | Action | GB | Unfinished | 1.2 | 07 Jan 2002 | EN |
