| OMEX AG | Zurich |
| Omicron Web-Services S.A. | Vaud |
| Omikron Data AG | Glarus |
| Omne Possibile | |
| Omni Ray AG | Zurich |
| Omnis - Olivier Müller Networks & Internet Services | Zurich |
| OMrun | Zurich |
| Omya AG | |
| Onchain Technologies AG | |
| Oncobit AG | |
| Oncompass GmbH | |
| Oncoteq AG | |
| One 4 You IT GmbH | Zurich |
| One Inside Switzerland AG | Basel-Landschaft |
| One Net GmbH | St. Gallen |
| Onebyte AG | Zurich |
| Oneconsult International AG | Zurich |
| Oneday AG | |
| Oneline | |
| Onena Medicines AG | |
| OneVisage S.A. | |
| Oniko AG | Aargau |
| Onlime GmbH | Zurich |
| Online Consulting AG | St. Gallen |
| Online Marketing AG | Zug |
| Online PC | Zurich |
| OnlineDoctor AG | |
| OnSpirix Ltd | Zug |
| OOIT.com AG | Zurich |
| Opacc Software AG | Lucerne |
| Open Net S.à.r.l. | Vaud |
| Open Systems AG | Zurich |
| Openconcept AG | Bern |
| Opendata.ch | |
| OpenLimit SignCubes AG | Zug |
| Openline GmbH | Basel-Stadt |
| OpenOlat | |
| Oper | |
| Opigno LMS | |
| Opna Bio S.A. | |
| Optimanet Schweiz AG | Zurich |
| Optimatik AG | Appenzell Ausserrhoden |
| Optimex IT-Services | Lucerne |
| Optimiso Group S.A. | Geneva |
| Optimo Medical AG | |
| Option 4.0 AG | |
| Option-Web.ch | Valais |
| Optiprint AG | St. Gallen |
| Optive AG | Thurgau |
| OQTACORE S.à.r.l. | |