| ONTRAPORT | California |
| Ontrix.com | |
| OnTV Pittsburgh | Pennsylvania |
| Onur Kahraman, LLC | Wyoming |
| Onvego Ltd | |
| OnviSource, Inc. | Texas |
| Onward Internet Marketing | Minnesota |
| Onwire | California |
| OnWired, LLC | |
| onXmaps, Inc. | |
| ONY Biotech, Inc. | New York |
| OnYourMark, LLC | Wisconsin |
| Onyx | California |
| Onyx CenterSource | Texas |
| Onyx Graphics, Inc. | Utah |
| Onyx Optics, Inc. | California |
| Onyxia | New York |
| OnyxTec | |
| Onzra | California |
| Ooblec, LLC | |
| Oodle | |
| OOHology | |
| Ookla | Washington |
| Oomph, Inc. | |
| Oongawa Design, Inc. | |
| Oort, Inc. | Massachusetts |
| Oostas, LLC | |
| Oozle Media | Utah |
| Opal Camera, Inc. | |
| Opal Fuels | New York |
| Opal Labs, Inc. | Oregon |
| Opal Security | |
| Opal Therapeutics, Inc. | |
| OpalSoft, Inc. | California |
| Opanda Studio | Georgia |
| Opanga Networks, Inc. | Washington |
| Opango LMS | Texas |
| Opaque | |
| Opaque Systems, Inc. | California |
| Open Access BPO | Nevada |
| Open Approach | Vermont |
| Open AR Cloud | Oregon |
| Open Austin | Texas |
| Open Automation Software | Colorado |
| Open Bioinformatics Foundation | Massachusetts |
| Open Black Belt, LLC | Texas |
| Open Book Systems, Inc. | Massachusetts |
| Open Computer Project | California |
| Open Computing 4, Inc. | Connecticut |
| Open Connectivity Foundation | Oregon |