DEVELOPERS
- O.D.E.
- O-Two
- Ocarina System
- Ocean
- Ocean Entertaiment / Etrange Libellules
- Ocean / Power & Magic
- Ocean Software
- Octagon Entertainment
- Oddworld Inhabitants
- Odyssey Software Inc.
- OeRSTED
- Office Create
- Office Koukan
- Olympia
- Olympia / Heiwa
- Omega Force
- Omega Micott
- Omega Products
- Omiya Soft
- On Dimand
- One Man Band
- Onion Egg
- Onion Egg / JAM
- Onion Egg / Tose Software
- Onion Software
- Ontsu Soft
- Ooparts
- Open
- Open Book
- Open Sesame
- Open System
- Opensystem
- Opera House
- Opera House / Marchen Breaker
- Opus
- Opus Corp
- Opus Corp. / Bandit
- Oracion
- Oracion Inc
- Orbital Media, Inc.
- Origin
- Origin Systems
- Origin Systems / Lion Entertainment, Inc
- Ornith
- Orpheck Inc
- Osiris Software Design Studios, Inc
- Outback
- Outback / D.A.S.T
- OutLook Entertainment
- OutSide Directors Company
- Oxford Softworks
- OZ Club (Escot)
- Ozark Softscape