| om3 | HALCON Object Model 3D Data |
| omar | SOCSIM Output Marriage File |
| omb | Omnibus Offline Web Storage Data |
| omcs | Office Manager SQL Archive |
| omd | Routing J Server Data |
| omeg | Mathematica for Mac OMEG Data |
| omf | Routing J Server Routing Data |
| omf | Open Media Framework file |
| omfi | Open Media Framework file |
| omlog | CA OM Web Viewer Log |
| omm | OptiMatrix Maker Data |
| omn | Omnipotent Collection Text |
| omr | OMR Reader Template |
| oms | Order Maven Data |
| oms | LightShow Pro Optimized Media Sequence |
| omt | HLA Object Model Template |
| omu | eXtendable Wad Editor OMU Data |
| omx | hyperMILL CAM Temporary Calculation Data |
| omx | OMAX Routed Data File |
| onbatch | ON1 Photo Batch Data |
| ond | Lotus Notes Database |
| onebin | Microsoft OneNote Binary Data |
| onecache | Microsoft OneNote Cached Data |
| oneffects | Perfect Effects Effects Data |
| onepkg | Microsoft OneNote Package |
| onetmp | Microsoft OneNote Temporary File |
| onetoc | Microsoft OneNote Table of Contents |
| onetoc2 | Microsoft OneNote Table of Contents |
| onl | PATCHMASTER Online Analysis Information |
| onm | Outdoor Navigator Map |
