List Of All Extensions And Filetypes - O

This is an easy approach from me to give and describe each and every filetype and extension as much as possible.
here is the list for the information about various filetypes and extensions starting from alphabet O

Extension	Information
O	Xcode Compiled Core C or Assembler Program (Apple Inc.)
O	Origin C Compiled Program File (OriginLab Corporation)
O	Free Pascal Object FIle for Linux or DOS Version (FPC Development Team)
O	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
O	Executable and Linkable Format File
O	Object File
O	UNIX/GCC Object File
O$$	Output File
O$$	Sprint Outfile
O01	Typhoon Voice File
O1	Free Pascal Object File for GO321v1 Platform (FPC Development Team)
O1	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
O2C	Objects to See 3D File Format (mb Software AG)
O3	Ozone Messenger Program Support Files (htmlland.net)
O8O	Mediator5 Repositorytabs Vorlagen.006 File
OAB	Outlook Address Book (Microsoft Corporation)
OAF	ETH Oberon Applet File
OAF	Outrage Animation Rows
OAF	Flight Simulator Texture File (Microsoft Corporation)
OAH2DSK	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OARC	Optix Archive Bundle (mindwrap, inc.)
OARC	Optix Archive Manifest (mindwrap, inc.)
OAZ	NetFax Manager OAZ Fax File
OB	IMB LinkWay Object File
OB	ABF Outlook Backup Backup File (ABF software, Inc.)
OB!	Orbit Downloader Incomplete Download (OrbitDownloader.com)
OB$	Compressed OBJ (Microsoft Corporation)
OB1	OzWin CompuServe E-mail/Forum Access Saved Outbox File
OB3	ORTIM Zeit Data (ORTIM Industrial Engineering Deutschland GmbH)
OB3	Outlook Backup Full Backup File (ABF software, Inc.)
OBA	Timespace X100 Digital Video Recorder Video File (Timespace Technology Ltd.)
OBD	Office Binder Document (Microsoft Corporation)
OBD	Oracle Forms Online Help File (Oracle)
OBE	Out Of Box Experience
OBE	System DLL Oobe File
OBJ	Wavefront 3D Object
OBJ	Relocatable Object Code
OBJ	Blender 3D Object (The Blender Foundation)
OBJ	LightWave 3D Object (NewTek)
OBJ	Hyperion-CADRazor 3D Model (TITAN Algorithms)
OBJ	UVMapper Object (Stephen L Cox)
OBJ	Metatools Object Bryce Support File
OBJ0	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OBJ1	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OBJECTS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OBK	Ubi Soft Chessmaster Opening Book File
OBK	Oxygen Phone Manager Phone Book (Oxygen Software)
OBML	Opera Mini Saved Web Page (Opera Software ASA)
OBN	Oberon-2 Module Source File
OBP	Bryce 5 Object Preset (DAZ Productions)
OBPACK	ObjectBar Object Package (Stardock Corporation, Inc.)
OBR	Objective Reference Document Link (Objective Corporation Limited)
OBR	C++ Object Browser Data File (Borland Software Corporation)
OBS	OzWin CompuServe E-mail/Forum Access Saved Outbox File
OBS	ObjectScript Script
OBSKIN	ObjectBar Skin File (Stardock Corporation, Inc.)
OBT	Office Binder Template (Microsoft Corporation)
OBTHEME	ObjectBar Theme File
OBTHEME	ObjectBar Theme File (Stardock Corporation, Inc.)
OBV	ObjectScript Visual Interface
OBX	OpenBook OpenBook 8.0 Document File (Freedom Scientific, Inc)
OBX	Rational XDE (IBM)
OBZ	Office Binder Wizard (Microsoft Corporation)
OC8	OrgCon 8 Organization (EcoMerc)
OC9	OrgCon 9 Organization (EcoMerc)
OCA	Control Typelib Cache (Microsoft Corporation)
OCA	OLE Custom Control Library Information
OCA	Visual Basic Control Typelib Cache
OCB	Origin Precompiled Origin C File (OriginLab Corporation)
OCC	OptControlCentre Model File
OCC	DB/TextWorks Database Terms and Words (Inmagic, Inc.)
OCCSAN	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OCD	OCAD Digitized Map (Steinegger Software)
OCD	OrgCon 7 Organization (EcoMerc)
OCE	Brio Query (Hyperion Solutions Corporation)
OCEN	EdGCM Data File (The EdGCM Cooperative Project of Columbia University)
OCF	Object Craft File
OCF	OM2Cipher File
OCI	openCanvas Image (System Products Co., Ltd.)
OCM	Netscape Communicator Aim File
OCM	Internet Odyssey 2 Update
OCM	AOL Advertising Control File (America Online, Inc.)
OCN	OneCable.net - Explorer Measurement Data File (OnTimeLine)
OCP	Offline Commander Project File
OCP	Advanced Art Studio
OCR	FAXGrapper FAX Text File
OCS	eDoc DigiSign Digitally Signed Document (Fujitsu Denmark)
OCSP	Optix Scanner Plug-in (mindwrap, inc.)
OCT	Octalizer Musical File
OCT	Radiance Octree Format
OCTOPUSFONT	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OCX	Object Linking and Embedding (OLE) Control Extension (Microsoft Corporation)
OC_	Doko Compressed Install File
OD1	Omnis5 Database File
OD2	Omnis5 Database File
OD3	Omnis5 Database File
OD4	Omnis5 Database File
OD5	Omnis5 Database File
OD6	Omnis5 Database File
OD7	Omnis5 Database File
OD8	Omnis5 Database File
OD9	Omnis5 Database File
ODA	ODA Document
ODA	Used with OCX
ODA	AIBO Audio Voice (Sony)
ODA	CALS Group IV Type 2 Raster Image
ODB	OpenOffice/StarOffice OpenDocument (Ver 2) Database (Sun Microsystems, Inc.)
ODB	ABAQUS File (ABAQUS, Inc.)
ODB	Organizers Database (ODB) Database (Organizers' Collaborative)
ODB	ArcView Object Database ASCII File (ESRI)
ODB	Abaqus/CAE Binary Output File (Dassault Systèmes)
ODB	Psion Organiser Datafile and LZ Diary File (Psion PLC)
ODC	Office Data Connection
ODC	OpenOffice/StarOffice OpenDocument (Ver 2) Chart (Sun Microsystems, Inc.)
ODCCUBEFILE	Office Data Connection
ODCDATABASEFILE	Office Data Connection
ODCNEWFILE	Office Data Connection
ODCTABLEFILE	Office Data Connection
ODD	Coby Voice Recorder Format (Coby Electronics Corp.)
ODDS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ODE	Office Object Data Embedding File (Microsoft Corporation)
ODF	OnkoS Data (OnkoS)
ODF	Open Document Interchange (ODIF)
ODF	BattleZone Cartographers Guild File
ODF	OpenOffice/StarOffice OpenDocument (Ver 2) Formula (Sun Microsystems, Inc.)
ODF	Star Trek Armada Ship/Structure Infomation
ODG	OpenOffice/StarOffice OpenDocument (Ver 2) Graphics Document (Sun Microsystems, Inc.)
ODH	Odigo History File (Comverse, Inc. a part of Comverse Technology)
ODI	OpenOffice/StarOffice OpenDocument (Ver 2) Image (Sun Microsystems, Inc.)
ODIF	Open Document Interchange Format
ODL	Object Definition Language
ODL	Visual C++ Type Library Source (Interface Definition Language File) (Microsoft Corporation)
ODM	Opendisc Software (Opendisc)
ODM	OverDrive Media Console Media Control File (OverDrive Inc.)
ODM	OpenOffice/StarOffice OpenDocument (Ver 2) Global Text Document (Sun Microsystems, Inc.)
ODMP	Optix Collection Package (mindwrap, inc.)
ODOCK	ObjectDock Theme (Stardock Corporation)
ODP	Analytics Parameters for Analysis Services (Actuate Corporation)
ODP	OpenOffice/StarOffice OpenDocument (Ver 2) Presentation (Sun Microsystems, Inc.)
ODP	Oedipus
ODS	Outlook Express Mailbox (Microsoft Corporation)
ODS	NCompass Labs Internet Script
ODS	OpenOffice/StarOffice OpenDocument (Ver 2) Spreadsheet (Sun Microsystems, Inc.)
ODS#	OpenOffice/StarOffice OpenDocument (Ver 2) Open Spreadsheet (Sun Microsystems, Inc.)
ODT	OpenOffice/StarOffice OpenDocument (Ver 2) Text Document (Sun Microsystems, Inc.)
ODT	MindRender Virtual Reality Explorer Kit (VREK) Object File Format (Themekit Systems Ltd.)
ODU	Odigo User File (Comverse, Inc. a part of Comverse Technology)
ODZ	IBM OpenDoc Editor Package File
OEB	Open eBook Document (International Digital Publishing Forum (IDPF))
OEB	Outlook Express Backup Wizard
OEM	OEM Data Used During Device Install
OEM	SB_AWE Keys SB_NT File
OEM	Text Listing of Supported OEM Devices for WinNT
OF	LessDATA Video System OneFile File
OF	Audio Utility Tuningwrench Compressed File
OF	MicroImages Outline Font (MicroImages, Inc.)
OFASTER	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OFC	Open Financial Connectivity File
OFD	ObjectView Form Defintion
OFD	20-20 Office Sales E-magine File (20-20 Technologies)
OFD	OfficeForms Form Data File (Toplevel Computing)
OFF	3D Mesh Object File Format
OFF	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OFF	Vector Graphic
OFFENSE	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OFFICES	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OFL	OtsTurntables Playlist (Ots Labs)
OFM	OfficeForms Blank Form File (Toplevel Computing)
OFM	PostScript Font Description File
OFM	Embroidery Design File
OFM	Font (Adobe Systems Incorporated)
OFM	OmniForm Form File (Nuance Communications, Inc.)
OFN	Office FileNew File (Microsoft Corporation)
OFN	Systems Management Server (SMS) Offer Creation Notification (Microsoft Corporation)
OFR	OptimFROG Encoded Audio (Florin Ghido)
OFR	Systems Management Server (SMS) Offer Description File (Microsoft Corporation)
OFT	Outlook Item Template (Microsoft Corporation)
OFW	Toplevel Forms Form (Toplevel Computing Ltd)
OFX	Open Financial Exchange File
OFX	Olicom Fax
OGA	Ogg Vorbis Audio Profile (Xiph.Org Foundation)
OGF	OnkoS Graphic File (OnkoS)
OGF	Outrage Graphic Rows
OGF2	MapViewGPS Map Coordinates File
OGF3	MapViewGPS Map Coordinates File
OGG	Ogg Vorbis Codec Compressed Multimedia File (Xiph.Org Foundation)
OGG	Origin Graphic File (OriginLab Corporation)
OGG	Salt Lake City Game File
OGI	OpenPBX Gateway Interface File (OpenPBX.org)
OGL	Overlay Source Code
OGM	Ogg Vorbis Compressed Video File
OGM	Origin Matrix File (OriginLab Corporation)
OGNC	Web Page Source Code
OGO	Origin Pro Graphic Object File (OriginLab Corporation)
OGS	Origin Script File (OriginLab Corporation)
OGV	Ogg Vorbis Video Profile (Xiph.Org Foundation)
OGV	Theora Ogg Transport Stream Video File (Xiph.Org Foundation)
OGW	Origin Worksheet File (OriginLab Corporation)
OGX	C++ Component Gallery Exported Classes and Resources (Borland Software Corporation)
OGX	Ogg Vorbis Multiplex Profile (Xiph.Org Foundation)
OH	Overhoor ( DrillAssistant) List (Efkasoft)
OH4	Overhoor ( DrillAssistant) List (Efkasoft)
OHC	OpenHelp Table of Contents File (Borland Software Corporation)
OHI	OpenHelp Index (Borland Software Corporation)
OHL	OpenHelp Link (Borland Software Corporation)
OHP	DOS 7 File
OHP	OpenHelp Project File (Borland Software Corporation)
OHS	Bink Outbound History
OHSD	HealthFrame OpenHealth Service Plug-in (Records For Living, Inc.)
OHW	Overhoor ( DrillAssistant) List (Efkasoft)
OID	Prosa/OM Object Interaction Diagram
OID	ProCurve Manager Non-ProCurve Network Device File (Hewlett-Packard Development Company, L.P.)
OIF	QuickBase Web-sharable Database Interchange File
OIK	Lenné3D Plant Distribution File (Lenné3D GmbH i.G.)
OIL	Open Image Library Format
OIT	SleepScan and Ceegraph Offset Index File (Bio-logic Systems Corp.)
OIX	Lenné3D Plant Distribution File (Lenné3D GmbH i.G.)
OJP	3WayPack (The Three-Mode Company)
OK	Dot OK File Digest (John Oberschelp)
OK	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OKM	OkMap Map Defining File (Gian Paolo Saliola)
OKS	OKScript File (Mike Mardesich)
OKT	Oktalyzer Tracker Module
OKX	OKScript File (Mike Mardesich)
OLB	AUTOGEN
OLB	PSpice Capture Symbols Models (Cadence Design Systems, Inc.)
OLB	VAX Object Library
OLB	Medical Terminology Challenge Data File (Delmar Learning)
OLB	Automation Object Library (Microsoft Corporation)
OLB	OrCAD PSpice Capture Symbols Model (Cadence Design Systems, Inc.)
OLD	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OLD	Old Version
OLDEST	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OLE	Object Linking and Embedding (OLE) Object
OLF	OyezForms Legal Documents (UK) (Oyez)
OLG	OATS Log File (AmsterCHEM)
OLI	Olivetti Text File
OLK	Outlook Address Book (Microsoft Corporation)
OLK	MS Mail Mailbag Lock
OLL	TrialDirector Object Load List
OLL	TrialDirector Load File (inData Corporation)
OLLIEFONT	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OLN	Visual C++ Outline Examples (Microsoft Corporation)
OLR	Openlab Raw Format (Improvision)
OLRW	Openlab Raw Format (Improvision)
OLSR	olsrd Configuration (olsr.org)
OLT	Orbit Downloader List File (OrbitDownloader.com)
OLT	Visual C++ Outline Examples (Microsoft Corporation)
OLV	OnLive! Traveler Sound File (The Digital Space Commons)
OLV	OyezForms Legal Documents (UK) (Oyez)
OM	Omicron Compiler File
OMA	Sony OpenMG Music Format File (Sony Corporation of America)
OMB	Omnibus Offline Web Storage (Alfega Technologies, Inc.)
OMCS	Office Manager Enterprise Document Archive (Softwarebuero Krekeler)
OMD	Prosa/OM Class Model
OMF	Operation, Management & Finance Database (ENIAC Computing)
OMF	Open Media Format File
OMG	O&O DiskImage Disk Image (O&O Software GmBH)
OMG	OpenMG Jukebox (Sony)
OMN	Omnipotent, Inc. Collection File
OMO	Oracle Media Objects File
OMP	Office Manager Pro Document Archive (Softwarebuero Krekeler)
OMP	OpenMind Project (MatchWare A/S)
OMS	Omega Downloader Configuration File
OMS	Macintosh MP3 Music Format
OMS	Briggs Softworks Order Maven
OMX	Ots Media Library (Ots Labs Pty Ltd)
OMX	OMAX Make Tool Path File (OMAX Corporation)
ON	Audio Utility Tuningwrench Compressed File
ON	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OND	Notes Database (IBM)
ONE	OneNote Note File (Microsoft Corporation)
ONE	docPointer Visual ReadMe File (docPointer)
ONE	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ONE	SEMONE Compressed Archive
ONE	EdgeCAM Licensing Data Ffile (Pathtrace Engineering Systems)
ONF	Open Navigation Format File
ONLINE	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ONX	Onyx Graphics Postershop File
OO	Free Pascal Object File for OS/2 Version (FPC Development Team)
OOM	Shroom Swap File
OOP	OOP Packer Archive (TonyTown Software Ltd.)
OP	Origin Preprocessed Origin C File (OriginLab Corporation)
OP	Rescue Disk File
OP2	Outpost 2 Saved Game
OP2	Musplay 1.72 File
OP2	Stanford Research Systems Optimlelt File (Stanford Research Systems, Inc.)
OP2	NEi Nastran Binary Results Neutral File (Noran Engineering, Inc.)
OP73	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPA	Psion OPL Object File (Psion PLC)
OPC	Beta 44 Job File
OPC	Office Upgrade Control File (Microsoft Corporation)
OPC	Omron OPC Client File
OPD	OmniPage Document (Nuance Communications, Inc.)
OPD	Durango Interferometry Software Document (Diffraction International)
OPEN	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPENYOURMIND	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPF	KEPServerEX Project Configuration File (Kepware Technologies Inc.)
OPF	Visual OMP Project File (DNA Software, Inc.)
OPF	Obsidium Project File (Obsidium Software)
OPF	Gemstar eBook Publisher Package (Gemstar eBook)
OPF	Flip Album File
OPI	OmniPass Exported User (Softex, Inc.)
OPI	ExpressRecognition Server OCR Processing Information File (Adlib Software)
OPJ	Origin Project File (OriginLab Corporation)
OPJ	OmniPage Schedule (Nuance Communications, Inc.)
OPJ	OrCAD Project File (Cadence Design Systems, Inc.)
OPK	Origin Origin Pack File (OriginLab Corporation)
OPL	Psion Organiser Programming Language Source File (Psion PLC)
OPM	Quadrox Digital CCTV System Components
OPML	Outline Processor Markup Language
OPN	Court Opinion File (Tennessee Administrative Office of the Courts)
OPN	Rebel Strip Poker Opponent File (Rebel Software)
OPN	Exact Active Options
OPN	Strip Poker Deluxe Opponent File (Eagle Rock Enterprises, Inc.)
OPO	Psion OPL Output Executable File (Psion PLC)
OPO	Psion Organiser OPL Code (Psion PLC)
OPOS	VirtuaSys Opos Script (VirtuaSys :: Sistemas Virtuais)
OPP	IPhoto File (Keronsoft)
OPR	OPRO X Browser Print Report File (OPRO Japan Co.,Ltd.)
OPS	Office Profile Settings File (Microsoft Corporation)
OPS	Dynamite VSP Object Placement Style (3am Solutions (UK) Limited)
OPT	Developer Studio File Workspace Options (Microsoft Corporation)
OPT	QEMM Optimize
OPT	Business Integrator Option File (Pervasive Software Inc.)
OPT	Segue SilkTest Option Set File
OPT	Delphi Project Options (Borland Software Corporation)
OPT	ProWORX Nxt List Module Option File (Schneider Electric)
OPT	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPT	PhotoScore Document (Neuratron Ltd)
OPT	Psion Organiser OPL Source (Psion PLC)
OPT	pcAnywhere Option Set File
OPT	FLEXnet Manager Options File (Acresso Software Inc.)
OPT	Options/Configuration
OPTIONAL	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPTNS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPUS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OPW	OrgPlus Organization Chart (HumanConcepts, LLC)
OPX	OrgPlus Organization Chart (HumanConcepts, LLC)
OPX	OrgChart Organization Diagram (Microsoft Corporation)
OPX	Psion Organiser Programming Language (Psion PLC)
OPX	Exact Inactive Options
OPX	Flip Album File
OPX	OPL Extension DLL
OPY	OptiY Model (OptiY)
OQY	Excel OLAP Query File (Microsoft Corporation)
OR	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OR2	Organizer Ver 2 File (IBM)
OR3	Organizer 97 File (IBM)
OR4	Organizer (IBM)
OR5	Organizer (IBM)
OR6	Organizer Data File (IBM)
OR8	Rational Rose Oracle8 Database Model Report (IBM)
ORA	Oracle 7 Configuration
ORA	MyPaint Open Raster Image File (Open Raster)
ORC	cSound Synthesis Instruments (Csounders)
ORC	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ORC	Oracle 7 Script
ORC	Digital Orchestrator Plus Sound File (Voyetra Turtle Beach, Inc.)
ORCA	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ORD	BC45 Owl File
ORD	OMAX Make Tool Path File (OMAX Corporation)
ORD	Open Reminder Database (ITOpen.eu SOFTWARE)
ORE	Narbacular Drop Game Content (DigiPen Corporation)
ORE	3WayPack (The Three-Mode Company)
ORF	Olympus Digital Camera Raw Image File
ORF	Descent 3 Outrage Room Format
ORG	Organiser (IBM)
ORG	Odds Ratio Generator Data File (Psytek Ltd.)
ORG	Origin File (OriginLab Corporation)
ORG	Netmino File
ORG	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ORG	Yamaha Organ Flutes (Yamaha Corporation of America)
ORG	Hollywood FX Effects Organizer File (Pinnacle Systems, Inc.)
ORG	Microcal Origin Plot
ORGAN	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ORI	Original
ORI	Need for Speed-Hot Pursuit 2 File
ORIG	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
ORIG	Gen Original File
ORIGINAL	Netobjects Fusion Components BBScomp Message File
ORK	Warhammer: Mark of Chaos Game Archive (Games Workshop Group PLC)
ORM	Ormetis Workbench File (Ormetis S.A.S.)
ORMV	Ormetis View File (Ormetis S.A.S.)
ORO	3WayPack (The Three-Mode Company)
ORV	Oracom Video Format (Oracom Co. Ltd.)
OS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OS2	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OS3	OS/2 Warp 3 File
OSA	W32/Sober-AD
OSB	Sega Dreamcast Sound (One Shot Bank) (Sega of America, Inc.)
OSC	OptionScope Worksheet (Equis International)
OSC	Fruitypro Samples SS_effects File
OSC	Formula One 2001 Options File
OSC	Remote Installation Services Client Installation Wizard File (Microsoft Corporation)
OSD	Open Software Description File (Microsoft Corporation)
OSD	SoftGrid Program Description (Softricity, Inc.)
OSD	Directory Opus Configuration File (GPSoftware)
OSDX	Windows Search Connector (Microsoft Corporation)
OSF	ICZ OriSAFE
OSF	Distribution Bin File
OSF	Virtual Ticket (MetaCommunications)
OSF	Opera Skin (Opera Software ASA)
OSF	Descent 3 Sound File (Outrage Entertainment)
OSG	OpenSceneGraph ASCII Native Format (OSG Community)
OSI	SunNet OSI Description File (Sun)
OSI	Osiris Database (The Shmoo Group)
OSL	OckamSoft Log File (Ockam Instruments, Inc.)
OSMALLER	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OSp	On-Screen Takeoff (On Center Software, Inc.)
OSS	Office Saved Search (Microsoft Corporation)
OST	On-Screen Takeoff Project (On Center Software, Inc.)
OST	Outlook Offline Storage File (Microsoft Corporation)
OST	Exchange Offline Cache (Microsoft Corporation)
OST	Tivoli Storage Manager File (IBM)
OSTANDARD	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OTB	Nokia Phone Graphics Editor (Nokia)
OTB	On-the-air Bitmap
OTC	OpenOffice/StarOffice OpenDocument (Ver 2) Chart Template (Sun Microsystems, Inc.)
OTF	OnkoS Text Data File (OnkoS)
OTF	Open Type Font Format
OTF	Blu-ray Text Subtitle Font Information (Blu-ray Disc Association)
OTF	OpenOffice/StarOffice OpenDocument (Ver 2) Formula Template (Sun Microsystems, Inc.)
OTG	OpenOffice/StarOffice OpenDocument (Ver 2) Graphics Document Template (Sun Microsystems, Inc.)
OTH	OpenOffice/StarOffice OpenDocument (Ver 2) HTML Text Template (Sun Microsystems, Inc.)
OTH	Origin Graph Properties File (OriginLab Corporation)
OTH	Power Toys Other Folder Explorer Tool
OTHERFOLDER	Power Toys Other Folder Explorer Tool
OTHERS	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OTI	OpenOffice/StarOffice OpenDocument (Ver 2) Image Template (Sun Microsystems, Inc.)
OTL	Ventura Publisher's Type Foundry Outline Editor format
OTL	Z-Soft Type Foundry Font
OTL	Fookes Super NoteTab Template File
OTL	NoteTab Outline
OTL	OpenTrap Event Log
OTM	Micro Cookbook File (IMSI/Design LLC)
OTM	Origin Matrix Template File (OriginLab Corporation)
OTM	Outlook VBA Module (Microsoft Corporation)
OTM	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OTM2	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OTN	OmniPage Training File (Nuance Communications, Inc.)
OTO	Autopano Project (Alexandre Jenny)
OTOSET	OTOsuite Settings (GN Otometrics)
OTP	Top Secret Crypto Gold One Time Pad Key File (TAN$TAAFL Software Company)
OTP	Origin Graphic Template File (OriginLab Corporation)
OTP	OpenOffice/StarOffice OpenDocument (Ver 2) Presentation Template (Sun Microsystems, Inc.)
OTRKEY	OnlineTvRecorder Encoded Video (OnlineTvRecorder.com)
OTS	OtsJuke Sound File
OTS	PSR-9000 (Yamaha Corporation of America)
OTS	OpenOffice/StarOffice OpenDocument (Ver 2) Spreadsheet Template (Sun Microsystems, Inc.)
OTT	OpenOffice/StarOffice OpenDocument (Ver 2) Text Document Template (Sun Microsystems, Inc.)
OTT	Nokia Phone Ring Tone (Nokia)
OTW	Origin Worksheet Template File (OriginLab Corporation)
OTX	Olivetti Olitext Plus File
OU!	OzWin CompuServe E-mail/Forum Access Outbound Messages Online
OUD	Adlib ExpressRecognition Server User Defined Dictionary (Adlib Software)
OUT	PSpice Output File (Cadence Design Systems, Inc.)
OUT	Wireshark Traffic Log (Gerald Combs)
OUT	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OUT	NovaBACKUP Backup Set (NovaStor Corporation)
OUT	NEi Nastran Tabular Output File (Noran Engineering, Inc.)
OUT	OzWin CompuServe E-mail/Forum Access Outbound Messages
OUT	MyInfo Documnet/Outline (Milenix Software)
OUT	3WayPack (The Three-Mode Company)
OUT	Outlines or Output File
OUT	Pro/ENGINEER Temporary File (PTC)
OUTPUT	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OUV	Sphinx Open Ended Responses (Le Sphinx Développement)
OUX	PCCharge File (VeriFone)
OV	OpenInsight Database Overflow File (Revelation Software)
OV	OrgPlus OrgViewer File (HumanConcepts, LLC)
OV1	Program File - Overlay
OV2	Program File - Overlay
OV2	TomTom Point of Interest File (TomTom International BV)
OV3	Program File - Overlay
OVA	Sierra Web Studio Graphic
OVA	Web Studio Project Page (Back To The Beach Software, LLC)
OVB	OnkoS Vocabulary Backup File (OnkoS)
OVD	OverDisk Disk Use Database (Elias Fotinis)
OVD	ObjectVision Datafile (Application) (Borland Software Corporation)
OVE	Cakewalk Overture Score (Cakewalk)
OVER	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OVL	RollerCoaster Tycoon Program Sprite (Infogrames Entertainment SA)
OVL	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OVL	PDP-10 Overlay (Pre-Virtual Memory)
OVL	Program File - Overlay
OVLDEF	Gestionnaire d'extensions Overload Definition (Définition de surcharge) (Francis Gagné)
OVM	BHV Tonstudio Platin File
OVR	Program File - Overlay
OVW	Cool Edit Pro Overview File
OVW	Cubase .WAV File Image (Steinberg)
OVW	DIANA Overview File
OVX	Psion Oval Control (Psion PLC)
OW	Free Pascal Object File for Windows Version (FPC Development Team)
OWC	OutWit Hub OutWit Catch db Format (OutWit Technologies)
OWD	OpenWire Project
OWF	OnkoS Wave Data File (OnkoS)
OWG	OutWit Hub OutWit Gear db Format (OutWit Technologies)
OWL	BC45 Owl File
OWLING	Unknown Apple II File (found on Golden Orchard Apple II CD Rom)
OWM	OutWit Hub OutWit Mashup XML Format (OutWit Technologies)
OWS	Web Studio Project File (Back To The Beach Software, LLC)
OX	Ox Object-Oriented Matrix Programming Language File
OXB	OlapX Report Portfolio (OlapX Software)
OXC	OlapX Cube Definition File (OlapX Software)
OXL	OMEGA Product Suite File
OXO	DB-MAIN Compiled Voyager-2 Program
OXO	Ox Object-Oriented Matrix Programming Language File
OXT	OpenOffice.org Extension (OpenOffice.org Community)
OXV	OlapX Local View File (OlapX Software)
OYB	Organize Your Beanie Babies Data File
OYZ	Lotus Approach Alternate dBASE Index
OZF	Mozart Programming System Functor (Mozart Board)
OZF2	OziExplorer Map (Des & Lorraine Newman)
OZFX3	OziExplorer Image File (Des & Lorraine Newman)
OZM	Sharp Organizer Memo Bank
OZP	Sharp Organizer Telephone Bank
OZV	ORTIM Zeit Project (ORTIM Industrial Engineering Deutschland GmbH)