| Game | Rating | Download |
|---|
| O2 (version 4.18) |   | |
| OB68K1A Single Board Computer | | |
| Oba-Oba (set 1) | | |
| The Ocean Hunter | | |
| Ocha-Ken Hot Medal | | |
| Octane (Version 6.5 Rev 4.9 05/22/03) | | |
| LSI Octopus | | |
| Odin | | |
| Odin De Luxe | | |
| Odisea Paris-Dakar | | |
| Odyssey | | |
| Office Yeo In Cheon Ha (version 1.2) | | |
| Ironman Ivan Stewart's Super Off-Road (rev 4) | | |
| Off Road Challenge (v1.63) | | |
| Ironman Ivan Stewart's Super Off-Road Track-Pak - MAME machi... | | |
| Offroad Thunder | | |
| Off the Wall (2/3-player upright) | | |
| Oh My God! (Japan) | | |
| Oh! Paipee (Japan 890227) | | |
| Oinori-daimyoujin Matsuri | | |
| Oishii Puzzle Ha Irimasenka | | |
| Ojanko Yakata 2bankan (Japan) | | |
| Ojanko Club (Japan, Program Ver. 1.3) | | |
| Ojanko High School (Japan) | | |
| Ojanko Yakata (Japan) | | |
| Ojousan (Japan 871204) | | |
| Okeah-240 | | |
| Oriental Legend Super / Xiyou Shi E Chuan Super (ver. 101, K... | | |
| Oriental Legend 2 (Korea) / Xiyou Shi E Chuan Qunmoluanwu (W... | | |
| Oli-Boo-Chu | | |
| Olympian Games (Russia) | | |
| Olimpic Hockey (EM Bubble Hockey, set 1) | | |
| Ollie King (GDX-0007) | | |
| Olympia BOSS D | | |
| Olympus (Z Games, version 10) | | |
| Olympic Games | | |
| Olympus | | |
| People PC | | |
| Olympia Olytext 20 | | |
| Omega | | |
| Omega Fighter | | |
| Omega Race (set 1) | | |
| Omni (Shuffle) (L-1) | | |
| Omotesandou (Japan 890215) | | |
| OMTI 8621 ESDI/floppy controller (ISA) | | |
| Ondra | | |
| One For All (0101503V, New Zealand) | | |
| One Shot One Kill | | |
| One + Two | | |
| Onna Sanshirou - Typhoon Gal | | |
| OOPArts (prototype, joystick hack) | | |
| Opa Opa (MC-8123, 317-0042) | | |
| Konami's Open Golf Championship (ver EAE) | | |
| 2 On 2 Open Ice Challenge (rev 1.21) | | |
| OPlayer Mobile Game Console (MGS03-white) (Family Sport 100-... | | |
| Open Sesame (0351309, US) | | |
| Operation: Thunder | | |
| Operation Tiger (Ver 2.14 O) | | |
| Operation Wolf (World, set 1) | | |
| Operation Wolf 3 (World) | | |
| Orange Club - Maruhi Kagai Jugyou (Japan 880213) - MAME mach... | | |
| Orao 102 | | |
| Oriental Beauty (10213511, NSW/ACT) | | |
| Orbit | | |
| Orbit 1 | | |
| Orbit 9090 - The Dance Planet | | |
| Orbite (prototype) | | |
| Orbitor 1 | | |
| Orbitron | | |
| Orbs (10/7/94 prototype?) | | |
| Orchid Mist (0200849V, NSW/ACT) | | |
| Ordenador-TV (Spain) | | |
| Ordisavant (France) | | |
| Ordyne (World) | | |
| Oric 1 | | |
| oric_jasmin | | |
| oric_microdisc | | |
| Orion 128 | | |
| Oriental Legend 2 (V104, Oversea) | | |
| Oriental Legend / Xiyou Shi E Chuan (ver. 126) - MAME machin... | | |
| OutRunners (World) | | |
| Rabbit Printer (model OS-214) | | |
| osa_analyst | | |
| osa_maestro | | |
| osa_maestroa | | |
| osa_sparc | | |
| Executive | | |
| Osborne-1 | | |
| Psycho-Nics Oscar (World revision 0) | | |
| Oscar (0200348V, NSW/ACT) | | |
| Osman (World) | | |
| Disco Mahjong Otachidai no Okite (Japan) | | |
| Off The Charts (Russian) | | |
| Othello (version 3.0) | | |
| Othello Shiyouyo (J 980423 V1.002) | | |
| Othello Derby (Japan) | | |
| Operation Thunderbolt (World, rev 1) | | |
| Otomedius (ver GGG:J:A:A:2008041801) | | |
| Otona no Mahjong (Japan 880628) | | |
| The Oregon Trail | | |
| OutTrigger | | |
| Off the Wall (Sente) | | |
| Mahjong Ougon No Hai | | |
| Outback Jack (20195211, NSW/ACT) | | |
| The Outfoxies (World, OU2) | | |
| Outlaw [TTL] | | |
| OutRun 2 (Rev A) (GDX-0004A) | | |
| OutRun 2 SP SDX | | |
| OutRun 2 Special Tours (Rev A) (GDX-0014A) | | |
| Out Run (sitdown/upright, Rev B) | | |
| Out Zone | | |
| Over Drive (set 1) | | |
| Over Rev (Model 2C, Revision A) | | |
| Over Top | | |
| Owl Capone (10008711, NSW/ACT, Show Program) | | |
| Wizard OZ-750 | | |
| Ozma Wars (set 1) | | |
| Ozon I | | |
