| | Operation: Thunder | 1992 | Gottlieb | opthund | | 0.00 |
| | Option 3 (v1.0) (Datapak) (MPU4 Video) (clone of: v4opt3) | 1991 | Barcrest | v4opt3d | | 0.00 |
| | Option 3 (v1.0) (MPU4 Video) | 1991 | Barcrest | v4opt3 | | 0.00 |
| | Options Unlimited (Barcrest) (MPU3) | 1969 | Barcrest | m3optunl | | 0.00 |
| | Oracle (Bellfruit) (Dutch) (Scorpion 1) | 1969 | BFM/ELAM | sc1orac | | 0.00 |
![Orange Club - Maru-hi Ippatsu Kaihou [BET] (Japan 880221)](../snapsmall/MS_2430.html) | Orange Club - Maru-hi Ippatsu Kaihou [BET] (Japan 880221) (clone of: orangec) | 1988 | Daiichi Denshi | orangeci | Tabletop / Mahjong *Mature* | 0.00 |
| Orange Club - Maruhi Kagai Jugyou (Japan 880213) | 1988 | Daiichi Denshi | orangec | Tabletop / Mahjong *Mature* | 0.00 |
| | Orbatak (prototype) | 1969 | | orbatak | | 0.00 |
 | Orbit | 1978 | Atari | orbit | Shooter / Field | 9.26 |
| | Orbit 1 | 1978 | Hankin | orbit1 | | 9.27 |
| | Orbitor 1 | 1982 | Stern | orbitor1 | | 6.03 |
| Orbitron | 1982 | Signatron USA | orbitron | Shooter / Command | 6.67 |
| | Orbs (10/7/94 prototype?) | 1994 | American Sammy | orbs | | 0.00 |
 | Ordyne (Japan) (clone of: ordyne) | 1988 | Namco | ordynej | Shooter / Flying Horizontal | 0.00 |
| Ordyne (Japan, English Version) | 1988 | Namco | ordyne | Shooter / Flying Horizontal | 8.53 |
| | Oriental Diamonds (Barcrest) (German) (MPU4) | 1969 | Barcrest | m4ordmnd | | 0.00 |
 | Oriental Legend / Xi You Shi E Zhuan (ver. 105, Korean Board) (clone of: orlegend) | 1997 | IGS | orlegend105k | | 0.00 |
| Oriental Legend / Xi You Shi E Zhuan (ver. 111, Chinese Board) (clone of: orlegend) | 1997 | IGS | orlegend111c | | 0.00 |
| Oriental Legend / Xi You Shi E Zhuan (ver. 112) (clone of: orlegend) | 1997 | IGS | orlegende | | 0.00 |
| Oriental Legend / Xi You Shi E Zhuan (ver. 112, Chinese Board) (clone of: orlegend) | 1997 | IGS | orlegendc | | 0.00 |
