| ON1 | Oregon |
| ON24, Inc. | California |
| On3 | Wisconsin |
| Onapsis, Inc. | Massachusetts |
| Onbe | Illinois |
| OnBlick | Texas |
| Onboard Data, Inc. | Massachusetts |
| Onboard Systems International, LLC | Washington |
| Oncade | |
| OnCalla Solutions | Wyoming |
| OnCampus Advertising, LLC | |
| Once Accounting | |
| Once Interactive, Inc. | |
| ONCE Ventures | California |
| OnceHub | Delaware |
| Oncely | |
| Oncept Consulting Group | California |
| Onchilles Pharma, Inc. | |
| Onclusive, Inc. | |
| OncoC4 | Maryland |
| Oncocyte Corporation | California |
| Oncogenuity, Inc. | Florida |
| Oncoheroes Biosciences | |
| Oncoheroes Biosciences, Inc. | Massachusetts |
| Oncohost | |
| OncoLux, Inc. | |
| Oncolys BioPharma, Inc. | |
| Oncolyze, Inc. | |
| OnCom Corporation | New York |
| OncoNano Medicine, Inc. | Texas |
| Onconaut Therapeutics, Inc. | |
| Onconetix, Inc. | Ohio |
| OncoPep, Inc. | Massachusetts |
| OncoResponse | Texas |
| OnCorps, Inc. | Massachusetts |
| OncoSenX | Washington |
| OncoSTING, LLC | |
| OncoSynergy | Connecticut |
| OncoTAb, Inc. | North Carolina |
| OncoTartis, Inc. | New York |
| Oncotelic, Inc. | |
| ONCOtherapeutics, Inc. | |
| Oncotherapy Solutions, LLC | |
| ONCOTracker, Inc. | California |
| Oncoverity, Inc. | |
| Oncovir, Inc. | |
| Oncovolution | Massachusetts |
| OnCusp Therapeutics | |
| Ondeck | |
| One AI | California |