| Certific OÜ | |
| Change Ventures | Harju |
| ChangeAgain OÜ | |
| CINDX | |
| CIVITTA | |
| Cleveroad | |
| Cleveron AS | |
| Clinical Accelerator | |
| CM Games | |
| Co-One | |
| Codeborne OÜ | |
| Codelab Solutions OÜ | Harju |
| Cognitiwe | |
| CoinMetro OÜ | |
| CoinsPaid | |
| Comistar Estonia | |
| Commuun OÜ | Harju |
| Comodule OÜ | |
| Computernik OÜ | Harju |
| Connect IT OÜ | Harju |
| Connected Health | |
| Connected OÜ | Harju |
| Cookie3 | |
| Copymax OÜ | Harju |
| Cora Health | |
| CostPocket | |
| Coverler | |
| CRM Süsteemid OÜ | Harju |
| Crowdestor | |
| Crowdin | |
| Crypt.ee | |
| Crypto Snack OÜ | |
| Cryptopay Ltd | |
| Crystalspace OÜ | Tartu |
| Customer.guru | |
| Cyberarch Consulting | Harju |
| CyberLab.Team OÜ | Harju |
| Cyberlands.io OÜ | |
| Cybernetica | Harju |
| CYBERS | |
| CybExer Technologies | |
| Cyphergram | |
| Daniliants Ventures OÜ | |
| Dashbird | |
| Dashbouquet Development, LLC | |
| Data Service OÜ | Harju |
| Data-Xata | Harju |
| DataCatering OÜ | Harju |
| DataCumulus OÜ | |
| Datafox | |