Group
- Off the Page Games16
- Off the Page Games Ltd12
- Offcut Games21
- Ohio Kimono2
- Ohio Kimono, LLC6
- Ohio Men of the Red Chest148
- Ohio War Kings12
- Oil and Rope Games1
- Old Curmudgeon Studios6
- Old Gamers Club2
- Old Gamers Club4
- Old Gamers Group8
- Old Guys2
- Old Heroes Never Die3
- Old School Publish Presents ACKS1
- Old Skull Publishing1
- On The Lamb2
- On The Lamb Games35
- One Day West Games4
- One More Turn Games9