| olg | Orbit Legend Data |
| olif | Open Lexicon Interchange Format |
| olk | Microsoft Outlook Address Book |
| olk14 | Microsoft Outlook for Mac Message Data |
| olk14category | Microsoft Office Outlook for Mac Category Data |
| olk14contact | Microsoft Office Outlook for Mac Contacts Data |
| olk14event | Microsoft Office Outlook for Mac Events Data |
| olk14group | Microsoft Office Outlook for Mac Group Data |
| olk14message | Microsoft Office Outlook for Mac Message Pointer |
| olk14msgsource | Microsoft Office Outlook for Mac Message Data |
| olk14note | Microsoft Office Outlook for Mac Note |
| olk14rule | Microsoft Office Outlook for Mac Rule Data |
| olk14signature | Microsoft Office Outlook for Mac Signature |
| olk14task | Microsoft Office Outlook for Mac Task Data |
| olk14uid | Microsoft Office Outlook for Mac UID Data |
| olk15event | Microsoft Office Outlook for Mac Events Data |
| oll | TrialDirector Batch Load Data |
| olm | Microsoft Office Outlook for Mac Database |
| ols | WinOLS OLS Data |
| olx | Open Learning XML Data |
| oly | Act! Opportunities Layout |
| oly | AFP Overlay Resource |
| om | STK Owner/Mission File |
| 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 |