| Atmosol | Arizona |
| Atmosphere Apps | Florida |
| AtnetPlus, Inc. | Ohio |
| AtoB | California |
| Atollo Services | California |
| Atom Bioworks, Inc. | North Carolina |
| Atom Computing, Inc. | California |
| Atom Power, Inc. | North Carolina |
| Atom.com | Illinois |
| Atomation | Missouri |
| Atomera | California |
| Atomic | California |
| Atomic Actions Group, Inc. | |
| Atomic AI | California |
| Atomic Canyon | |
| Atomic Computers and Design, LLC | |
| Atomic Data | Minnesota |
| Atomic Design | New York |
| Atomic Design & Consulting | Texas |
| Atomic FI, Inc. | |
| Atomic Games | Minnesota |
| Atomic Glue | |
| Atomic Honey | |
| Atomic Infotech, LLC | Washington |
| Atomic Interactive | |
| Atomic Media SEO | California |
| Atomic Object | Michigan |
| Atomic Object, LLC | Michigan |
| Atomic Robot, LLC | |
| Atomic Supply | |
| Atomicdust | Missouri |
| AtomicJar | New Jersey |
| Atomicorp | District of Columbia |
| Atomicweb, LLC | Maryland |
| Atomicwork, Inc. | |
| Atomist | California |
| Atomogy Corporation | California |
| Atomos Space | Colorado |
| AtomRain | California |
| Atoms | |
| Atomwise | California |
| ATON Computing, Inc. | New Jersey |
| ATop Digital | |
| Atossa Therapeutics, Inc. | |
| AtoZinIT | |
| atQor | California |
| atQuo | |
| ATR SmartProcedures | Texas |
| Atraverse Medical, Inc. | |
| Atre Group, Inc. | New York |