- Observis
- Ocean View Games
- Ocusweep
- OGOship
- Oikee
- OiOi Smart Space
- Olento Life
- Olet Ihana!
- Omago
- Omakirja
- Oma Panimo
- Omegawave
- One Hour Method
- Onerva
- Online Dynamics
- Onni Care
- On-Time Research Solutions Oy
- Oodles Solutions
- Ooolala
- Oppidoo
- Oppobot
- OptiWatti
- Optiwise
- Origin by Ocean
- Osgenic
- Oupet
- Oura
- Ovaa
- Oviku
- OVObots
- OYOs Games