| Onkologischer Schwerpunkt Stuttgart e.V. | |
| Online Akademie GmbH & Co. KG | North Rhine-Westphalia |
| Online Digital X GmbH & Co. KG | Hesse |
| ONLINE Industrieelektrik und Anlagentechnik GmbH | Lower Saxony |
| Online Marketing aus Düsseldorf | |
| Online Optimizer | |
| Online Software AG | Baden-Württemberg |
| Online Solutions Group GmbH | |
| ONLINE USV-Systeme AG | Bavaria |
| Online4Business GbR | North Rhine-Westphalia |
| Onlinefabrik Patrick Werner | Baden-Württemberg |
| Onlinemarketing Hatzak | |
| Onlinemarketing-Strategen.de | |
| Onlineoff GmbH | Bavaria |
| OnlyVision | |
| OnMaCon GmbH | Hamburg |
| Onmotion GmbH | |
| Ono Oonsulting GmbH | |
| onOffice Software GmbH | North Rhine-Westphalia |
| Onsoft Technologies GmbH | |
| OnStartupJobs | |
| Ontaris GmbH | North Rhine-Westphalia |
| Onveda GmbH | |
| Onventis GmbH | Baden-Württemberg |
| Onvice Internet & Groupware Consulting oHG | North Rhine-Westphalia |
| OofOne GmbH | |
| OOI – Nord Investment GmbH & Co. KG | |
| oomoxx media e.K. | Lower Saxony |
| OOP Solutions | |
| OPAL Associates Holding AG | Baden-Württemberg |
| OPAL – Operational Analytics GmbH | |
| Open as App GmbH | |
| Open Europe Consulting | |
| Open Mind Technologies AG | Bavaria |
| Open New Media GmbH | Rhineland-Palatinate |
| Open Source Business Alliance | |
| Open Telematic Platform | |
| Open Text Software GmbH | Bavaria |
| Open-Xchange AG | |
| OpenCage GmbH | |
| OpenCMS | North Rhine-Westphalia |
| Openfellas GmbH | Bavaria |
| OpenHealth Technologies Group | |
| openmediavault | |
| OpenProject | Berlin |
| OpenRheinRuhr e.V. | North Rhine-Westphalia |
| OpenSoft+ GmbH | Baden-Württemberg |
| openSUSE | Bavaria |
| OpenSynergy GmbH | Berlin |
| OpenTalk GmbH | |