| OpenTechSchool e.V. | Berlin |
| OpenUsability e.V. | Berlin |
| Operational Services GmbH & Co. KG | Hesse |
| Operations1 | |
| Operator Telekommunikation International AG | North Rhine-Westphalia |
| Operun GmbH | |
| Opetus Software GmbH | Hamburg |
| opneHAB Community | Hesse |
| opseo Holding B.V. | |
| opta data Abrechnungs GmbH | North Rhine-Westphalia |
| Opta Data Gruppe | North Rhine-Westphalia |
| Opti Medien Center, Gesellschaft für digitalen Medienservice mbH | Bavaria |
| OptiLab Inh. K.Lischewski e.K. | Hesse |
| OPTIMA Business Information Technology GmbH | Bavaria |
| OPTIMA packaging group GmbH | |
| OPTIMAL System-Beratung GmbH & Co. KG | North Rhine-Westphalia |
| Optimate GmbH | |
| Optimerch GmbH | North Rhine-Westphalia |
| optimise-it GmbH | |
| Optimized Traffic Systems Development GmbH | |
| Optimo Software GmbH | Baden-Württemberg |
| Optimum Software | Baden-Württemberg |
| OptiSoft GmbH | Baden-Württemberg |
| OptiSys Kommunikationslösungen GmbH | |
| Optitool GmbH | Bavaria |
| Optivo GmbH | Berlin |
| Optiware EDV GmbH | Hesse |
| Optiz Consulting Deutschland GmbH | |
| Optocomponents GmbH | Baden-Württemberg |
| Optocore GmbH | Bavaria |
| Optronis GmbH | Baden-Württemberg |
| OptWare GmbH | Bavaria |
| OPUS Business Solutions GmbH | Bavaria |
| OPUS Marketing GmbH | Bavaria |
| Opus One Recruitment GmbH | |
| OpusCapita Software GmbH | North Rhine-Westphalia |
| Oput | Baden-Württemberg |
| OQmented | |
| OR Technology | Mecklenburg-Vorpommern |
| ORA-IT Systeme GmbH | |
| Oracle Germany | Bavaria |
| Orange Mocca | North Rhine-Westphalia |
| Orangefluid GmbH | North Rhine-Westphalia |
| Orbem GmbH | |
| Orbis AG | Saarland |
| ORBIT Gesellschaft für Applikations- und Informationssysteme mbH | North Rhine-Westphalia |
| Orbit Logistics Europe GmbH | North Rhine-Westphalia |
| Orbit Recycling | |
| Orbit Software Laboratories GmbH | |
| Orbit Ventures GmbH | |