| Omnidoc | Seine-Saint-Denis |
| Omnilog | |
| Omniris Technologies | Drôme |
| Omny | |
| OMWAVE S.A.S. | Hauts-de-Seine |
| ON-X Groupe | Hauts-de-Seine |
| Onaya | Loire-Atlantique |
| Once Upon A Time | |
| Oncle Bill Micro Informatique | Ardèche |
| Oncodesign Precision Medicine | |
| Oncodesign Services | |
| OncoDiag | |
| Oncovita | |
| Oncrawl | |
| Ondatafine S.A.R.L. | Paris |
| Ondorse | |
| One Biosciences | |
| One Computer | Bouches-du-Rhône |
| One Conciergerie | |
| One Logic Consulting | |
| One More Thing Studio | |
| One Opérateur | Seine-Maritime |
| One System | Ain |
| One Time | |
| One.Tel | Paris |
| One2Net | Paris |
| OneFlash | |
| Onepark | |
| Onepilot | |
| ONERA | |
| OnlineCreation.me | Gironde |
| Onlineformapro S.A. | Haute-Saône |
| OnlineOrNot S.A.S.U. | |
| OnLogic | |
| Onoff app | |
| OnSpark | |
| Onxeo S.A. | |
| Onyx Informatique | Moselle |
| ooblada S.A.S. | Paris |
| Oodiva | Seine-Saint-Denis |
| Oodrive | Paris |
| Oolite | |
| Ooreka | |
| Op-Systems | Bas-Rhin |
| Op2Lysis | |
| Opale Systems | |
| Opaledata | Pas-de-Calais |
| Opalis'tic | Pas-de-Calais |
| OPALYTICA | |
| OPCoach S.A.R.L. | Haute-Garonne |