| osm | OpenStreetMap Map |
| ospx | Dell KACE Patch Definition FIle |
| oss | Microsoft Office Outlook Saved Search |
| ost | Microsoft Outlook Offline Folder File |
| osw | Powernet Waveform File |
| osz | OpenLP Service File |
| ot | TheWord Old Testament Text Module |
| otdr | Yokogawa OTDR Data |
| ote | Orbscan Treatment Export Data |
| oth | Origin Theme Data |
| otl | NoteTab Outline |
| otlb | Microsoft OLE Type Library |
| otn | OmniPage Training |
| otv | Rotor-Disc OTV Kit OTV Calibration Data |
| otx | theWord Encrypted Old Testament Text Module |
| otz | OpenLP Theme File |
| oub | Oubliette Data |
| oud | Adlib Express User Defined Dictionary |
| ouf | Otravi Unit Frames Data |
| out | Altair FEKO POSTFEKO ASCII Output Data |
| out | FAST Output Data |
| out1 | UltraEdit Outline Data |
| outb | FAST Binary Output Data |
| outjob | Altium Designer OutputJob Data |
| outline | FontTwister Letter Outline Data |
| ouv | Sphinx Open Ended Responses Data |
| oux | PCCharge Transaction Response XML File |
| ov | OpenInsight Overflow Data |
| ov1 | MS-DOS Overlay Data |
| ov2 | MS-DOS Overlay Data |
| ov2 | TomTom POI Database |
| ov3 | MS-DOS Overlay Data |
| ov4 | MS-DOS Overlay Data |
| ov5 | MS-DOS Overlay Data |
| ovb | OnkoS Vocabulary Backup Data |
