| OEM Horanet | Vendée |
| Off-Works | |
| OFF7, l'accélérateur du Groupe Ouest-France | |
| Office Formation | Haute-Garonne |
| OfficeEasy S.A.S.U. | Nord |
| OfficePartner | Haut-Rhin |
| OfficeXpress | Seine-Saint-Denis |
| OFIS Informatique | Métropole de Lyon |
| OGI | Aveyron |
| Ohayo | Nord |
| OHM Games | |
| Ohm Studio S.A.R.L. | Paris |
| oHRIS | Nord |
| OHweb | Haute-Garonne |
| OKINA | |
| Oklin | Yvelines |
| OKTEO | |
| OKTEY | Haute-Garonne |
| Oktos | |
| Old Skull Games | |
| Olea Medical S.A.S. | |
| oledcomm S.A.S. | Yvelines |
| Olfeo | Paris |
| Olivgraphic | Métropole de Lyon |
| Ollivier | |
| OLRAS | Meurthe-et-Moselle |
| Olynsoft | |
| OM Conseil | Yvelines |
| Ombrea | |
| OMEGA Informatique S.A.R.L. | Alpes-Maritimes |
| Omerin S.A.S. | Puy-de-Dôme |
| Omi | |
| Omicron | Hérault |
| Omnes Capital | |
| OMNES Education | Paris |
| Omniciel | Bouches-du-Rhône |
| Omnidoc | Seine-Saint-Denis |
| 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 |