.o Object file (unix - Atari - GCC)
.o$$ Outfile (Sprint)
.oaz Fax (NetFax Manager)
.ob Object cut/paste file (IBM LinkWay)
.obd MS Office Binder
.obj Object code (Intel Recolatable Object Module)
.obr Object browser data file (Borland C++)
.obs Script (ObjectScript)
.obv Visual interface (ObjectScript)
.oca Control Typelib Cache
.ocf Object Craft File (Object Craft)
.ocm AOL Advertising Control files
Internet Odyssey 2 Update
.ocp Advanced Art Studio
Offline Commander Project file
.ocr Incoming fax transcribed to text (FAXGrapper)
.oct Radiance Octree Format
.ocx OLE custom control
.odf Open Document Interchange
BattleZone Cartographers Guild file
Star Trek Armada Ship/Structure Infomation
.odl Type library source (Visual C++)
.odt OpenOffice OpenDocument text document
.oeb Outlook Express Backup Wizard
.ofc Open Financial Connectivity file
.ofd Form definition (ObjectView)
.off Object File Format vector graphics
.ofm Adobe font
.oft MS Outlook Item Template
.ofx Olicom Fax
Open Financial Exchange file
.ogg Ogg Vorbis Codec Compressed WAV file
.ogm Ogg Vorbis Compressed Video file
.okt Music (Oktalizer)
.olb Object library (VAX)
.old Backup file
.ole Object Linking and Embedding Object .oli Text file (Olivetti)
.omf Open Media file
.omg OpenMG Jukebox
.oms Briggs Softworks Order Maven
Macintosh MP3 Music Format
Omega Downloader Configuration file
.ond Lotus Notes-related file
.oom Swap file (Shroom)
.opd Omnipage file
.opf Flip Album file
.opl Psion Organiser Programming Language Source file
.opn Active options (Exact)
.ops Microsoft Office profile settings file
.opt Optimize support file (QEMM)
.opw Organization chart (Org Plus for Windows)
.opx Inactive options (Exact)
.or2 Lotus Organizer 2 file
.or3 Lotus Organizer 97 file
.or4 Lotus Organizer file
.or5 Lotus Organizer file
.ora Parameter file (Oracle)
.org Calendar file (Lotus Organizer)
.osd Open Software Description file
.oss MS Office Saved Search
.ost Microsoft Outlook Offline file
.otf Open Type Format
.otl Outline font description (Z-Soft Type Foundry)
.otx Text file (Olivetti Olitext Plus)
.out Output file
.ov1 Overlay file (part of program to be loaded when needed)
.ov2 Overlay file (part of program to be loaded when needed)
.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)
.ovw Cool Edit Pro Overviewfile
Cubase .WAV File Image
DIANA Overview file
.ows Web Studio 2 Project file
