O
| Ext. | Description | Used by |
|---|---|---|
| O$$ | Outfile | Sprint |
| O | Object file | UNIX - Atari - GCC |
| O01 | Typhoon vOice file | AWAVE |
| OAZ | Fax | NetFax Manager |
| OB | Object cut/paste file | IBM LinkWay |
| OBD | Microsoft Office Binder | MSOffice |
| OBJ | Compiled machine language code | |
| OBJ | Object code | Intel Relocatable Object Module |
| OBJ | Wavefront Object | |
| OBJF | Data | Triangle strips object |
| OBR | Object browser data file | Borland C++ |
| OBS | Script | ObjectScript |
| OBT | Microsoft Office Binder Template | MSOffice |
| OBV | Visual interface | ObjectScript |
| OBZ | Microsoft Office Binder Wizard | MSOffice |
| OCF | Object Craft File | Object Craft |
| OCD | OCAD Map File | OCAD |
| OCR | Incoming fax transcribed to text | FAXGrapper |
| OCT | Musical file | Pctalizer |
| OCX | New Custom Control's format in VB 4.0 | Visual Basic |
| OCX | OLE custom control | |
| ODB | OpenDocument database | OpenOffice.org Base |
| ODF | OpenDocument formula | OpenOffice.org Math |
| ODG | OpenDocument drawing | OpenOffice.org Draw |
| ODIF | Open Document Interchange Format | |
| ODL | Object Description Language | |
| ODL | Type library source | Visual C++ |
| ODM | OpenDocument master document | OpenOffice.org Writer |
| ODP | OpenDocument presentation | OpenOffice.org Impress |
| ODS | OpenDocument spreadsheet | OpenOffice.org Calc |
| ODT | OpenDocument text document | OpenOffice.org Writer |
| OFD | Form definition | ObjectView |
| OFF | Object File Format vector graphics file | |
| OFF | Object File Format vector graphics | |
| OFM | PostScript font description file | |
| OFN | Microsoft Office documents | Microsoft Office |
| OGG | Ogg multimedia container format | |
| OHB | Source | On Hand Basic |
| OHS | Outbound History | Bink/+ |
| OIF | QuickBase file format | |
| OKT | Music (8 channels) | Oktalyzer |
| OKT | Music format | Oktalyzer |
| OLB | Object library | VAX |
| OLD | Backup file | |
| OLI | Text file | Olivetti |
| OLSR | Configuration file | olsrd |
| OMA | Audio file | Labelgate CD 2, MAGIQLIP2 |
| OMG | Audio file | Sony compressed audio file (ATRAC3) |
| OMF | Open Media Framework | Avid Media Composer |
| OOF | Data | Outrage 3D Object Format (Descent) |
| OOG | Data | WEBOOGL 3D object |
| OOM | Swap file | Shroom |
| OPJ | Origin Project File | Origin version 4.1 and later |
| OPN | Active options | Exact |
| OPT | Options | name used by many programs for configuration information |
| OPT | Delphi project options | Borland Delphi |
| OPT | Optimize support file | QEMM |
| OPW | Organization chart | Org Plus for Windows |
| OPX | Inactive options | Exact |
| ORA | Parameter file | Oracle |
| ORC | Orchestra MIDI file | CSound |
| ORG | Calendar file | Lotus Organizer |
| ORG | Older Origin Project | Origin versions 4 or earlier |
| OTG | OpenDocument drawing template | OpenOffice.org Draw |
| OTB | Over-the-air bitmap graphics | |
| OTF | Subtitle font information for media content | Media players / software which support PGS subtitling |
| OTH | OpenDocument HTML document template | OpenOffice.org |
| OTL | Outline font description | Z-Soft Type Foundry |
| OTL | Ventura Publisher's Type Foundry Outline Editor format | |
| OTP | OpenDocument presentation template | OpenOffice.org Impress |
| OTS | OpenDocument spreadsheet template | OpenOffice.org Math |
| OTT | OpenDocument text document template | OpenOffice.org Writer |
| OTX | Text file | Olivetti Olitext Plus |
| OUT | Output file | |
| OUT | Design II for Windows Output file | |
| OV1 | Overlay file (part of program to be loaded when needed) | |
| OV2 | Overlay file (part of program to be loaded when needed) | TomTom Point of Interest |
| OVD | Datafile | ObjectVision |
| OVL | Overlay file (part of program to be loaded when needed) | |
| OVR | Overlay file (part of program to be loaded when needed) | |
| OXT | OpenOffice.org extension | OpenOffice.org |
Read more about this topic: List Of File Formats (alphabetical)