O
Object file (Unix)
O
Object file (Atari)
O
Object file (GCC)
OAS
Word processor document (Fujitsu OAS)(Japanese)
OAZ
Fax (NetFax Manager)
OB
Object cut/paste file (IBM LinkWay)
OBD
Binder template (Microsoft Office)
OBD
Binder (Microsoft Office)
OBJ
Object file
OBR
Object browser data file (Borland C++)
OBS
Script (ObjectScript)
OBV
Visual interface (ObjectScript)
OBZ
Binder Wizard (Microsoft Office)
OCF
Object craft file (Object Craft)
OCR
Transcribed fax-to-text file (FAXGrabber)
OCX
Object Linking and Embedding (OLE) custom control (Microsoft)
ODL
Type library source (Visual C++)
ODS
Mailbox file (Microsoft Outlook Express)
OFD
Form definition (ObjectView)
OFF
Object File (3D Mesh)
OFN
FileNew file (Microsoft Office)
OFT
Template (Microsoft Outlook)
OKT
Music module (MOD) (Oktalyzer)
OLB
Object Library (OLE) (Microsoft)
OLB
Object library (VAX)
OLD
Backup file (Generic)
OLE
OLE object
OLI
Text file (Olivetti)
OO1
Voice file (Typhoon)
OOGL
Object Oriented Graphics Library
OOM
Swap file (Shroom)
OPJ
Project file (Orcad Schematic Capture)
OPL
Organiser Programming Language source file (Psion/Symbian)
OPN
Active options (Exact)
OPO
Output executable file (OPL)
OPT
Developer Studio file (Microsoft)
OPT
Optimize support file (QEMM)
OPW
Organization chart (Org Plus for Windows)
OPX
Extension DLL (OPL)
OPX
Inactive options (Exact)
ORA
Parameter file (Oracle)
ORC
Script (Oracle 7)
ORG
Calendar file (Lotus Organizer)
OR2
Calendar file (Lotus Organizer 2)
OR3
Lotus Organizer 97 file
ORA
Configuration file (Oracle 7)
OSS
Search file (Microsoft Office)
OST
Offline file (Microsoft Exchange/Outlook)
OTL
Outline font description (Z-Soft Type Foundry)
OTL
Template file (Super NoteTab) (Fookes)
OTX
Text file (Olivetti Olitext Plus)
OUT
Output file (Microsoft C)
OV1
Overlay file
OV2
Overlay file
OVD
Datafile (ObjectVision)
OVL
Overlay file
OVR
Overlay file
O$$
Outfile (Sprint)