| Apple II 5.25 disk |  O'Riley's Mine | 1981 | Datasoft, Inc. Chatsworth, CA, USA |
| Sharp MZ-80K type-in | Obakeyashi Game | 1981 | Kohgaku-Sha Co.,Ltd. |
| DECO cass. | Ocean to Ocean Model DT-110 | 1981 | Data East Corp. Japan |
| Handheld game | Octopus Model OC-22 | 1981 | Nintendo Co., Ltd. Japan |
| Applied Concepts Great Game Machine mod. | Odin Edition - Master Reversi | 1981 | Applied Concepts, Inc. |
| Apple II 5.25 disk | Odyssey in Time | 1981 | Krell Soft. |
| Sharp MZ-80K type-in | Ohtani Othello | 1981 | ASCII Corp. Japan |
| Sharp MZ-80K type-in | Oicho Kabu II | 1981 | Dempa Shinbunsha Japan |
| Sharp MZ-80B type-in | Oicho-Kabu Land | 1981 | Dempa Shinbunsha Japan |
| Handheld game | Oil Gang | 1981 | Epoch Co., Ltd. Tokyo, Japan |
| Apple II 5.25 disk | Oil Rig | 1981 | CPU Soft. Computer Programs Unlimited |
| Coin-op Misc. game | Okashi Daisakusen | 1981 | NAMCO, Ltd. Japan |
| Bally Astrocade type-in | Old Bent Nose | 1981 | Fabris, Robert San Jose, CA, USA |
| TRS-80 type-in | Old Glory | 1981 | SoftSide Publications, Inc. |
| Apple II type-in | Old Glory | 1981 | SoftSide Publications, Inc. |
| Atari 400/800 type-in | Old Glory | 1981 | SoftSide Publications, Inc. |
| Apple II 5.25 disk | Oldorf's Revenge | 1981 | Highland Computer Services |
| Apple II 5.25 disk | Olympic Decathalon | 1981 | Microsoft |
| Arcade Video game | Omega Race Cocktail model Model 930 | 1981 | Midway Mfg. Co. Schiller Park, IL, USA |
| Arcade Video game | Omega Race Mini-Myte model Model 931 | 1981 | Midway Mfg. Co. Schiller Park, IL, USA |
| Arcade Video game | Omega Race Sit-Down model Model 894 | 1981 | Midway Mfg. Co. Schiller Park, IL, USA |
| Arcade Video game | Omega Race Upright model Model 929 | 1981 | Midway Mfg. Co. Schiller Park, IL, USA |
| Texas Instruments Speak & Read ext. | On the Track | 1981 | Texas Instruments |
| Apple II 5.25 disk |  Oo-Topos | 1981 | Sentient Soft. |
| Arcade Video game |  Operacion Defender | 1981 | Operamatic Spain |
| Apple II 5.25 disk | Operation Apocalypse | 1981 | SSI Strategic Simulations, Inc. 16685 |
| Fruit Machine | Oranges And Lemons (Bellfruit) | 1981 | Bell-Fruit Mfg. Co., Ltd. B.F.M. UK |
| Apple II 5.25 disk | Orbitron | 1981 | Sirius Soft., Inc. Sacramento, CA, USA |
| TRS-80 type-in | Orienteering at Jacque's Coulee | 1981 | SoftSide Publications, Inc. |
| Apple II type-in | Orienteering at Jacque's Coulee P | 1981 | SoftSide Publications, Inc. |
| TRS-80 disk | Original Adventure Model CS-3518 | 1981 | Creative Computing Soft. |
| Coin-op Misc. game | Oshaberi Ohm | 1981 | Kato Seisakujo Co., Ltd Japan |
| Sharp MZ-80K type-in | Otani Othello | 1981 | ASCII Corp. Japan |
| Microtan 65 soft. | Othello | 1981 | Microtanic Soft. |
| Radofin 1292 Advanced Programmable Video System cart. | Othello P | 1981 | Radofin Electronics Germany |
| Atari 2600 cart. | Othello Model 49-75162 | 1981 | Sears Chicago, IL, USA |
| Apple II 5.25 disk | Other Ventures #1: Classic Adventure Model 041-0106 | 1981 | Adventure International |
| Apple II 5.25 disk | Other Ventures #1: Classic Adventure Model 042-0106 | 1981 | Adventure International |
| TRS-80 cass. | Other Ventures #2: The Curse of Crowley Manor Model 010-0108 | 1981 | Adventure International |
| TRS-80 disk | Other Ventures #2: The Curse of Crowley Manor Model 012-0108 | 1981 | Adventure International |
