.??_  Files ending in "_" are often compressed install files of the same
          name (e.g., .EX_ expands to .EXE, .DL_ expands to .DLL, etc.)
  .M    Matlab Function
        Brief Macro Source
        Mathematica File
        Limbo Interface Declaration (Inferno OS)
        Cliq Accessories Datebook Modification File [Linux Suite PDF Description]
        Desktop Color Separation Specification Magenta Layer (usually an EPS file)
  .M_U  MazeGold Critical File Backup
  .M??  Ingres Modify Table/Index File (?? = Hex 00 to FF)
  .M$S  MindStor Firmware Update File (M$A$W.M$S)
  .M11  MASS11 Text File
  .M12  Proprietary Data Format for Interchange of Defense Form Data with Mil-Pac Technology Software Products (link is PDF file)
        S-BASIC File
        Hydrographs Synthesis Project File
        SHARP MZ-series Emulator File
  .M15  Apple MPEG-1 Video
  .M18  Accolade Golf Course File
  .M1A  Apple MPEG-1/2 Audio
  .M1V  MPEG-1 Video File
  .M2A  Apple MPEG-1/2 Audio
  .M2P  MPEG-2 Program Stream Format File
  .M2S  MPEG-2 Audio and Video (system stream)
  .M2V  MPEG-2 Video Only File
  .M3   Modula 3 Program File
  .M32  Dr.T MIDI File
  .M3A  MPEG Archive Enhanced .M3U Playlist File
  .M3D  3D Animations Macro
        Corel Motion 3D Animation
        EverQuest File
  .M3S  Myst III Exile Saved Game
  .M3U  MP3 Playlist File [WinAmp] [MattBatt iAM-player]
  .M4   UNIX M4 Preprocessor File
  .M75  Apple MPEG-1 Video
  .M8   Heretic II MipMap  [XnView]
  .MA   Maya File (ASCII)
        Diablo II Map File
  .MA3  Harvard Macro (Harvard Graphics taken over by Serif)
  .MAC  MacPaint Bitmap Graphic  [XnView]
        Macro (various)
  .MACP  MacPaint Bitmap Graphic  [XnView]
  .MAD  MS Access Module Shortcut [Buy Office XP at Shop.Microsoft]
        Game Movie File (unverified)
  .MAF  MS Access Form Shortcut [Buy Office XP at Shop.Microsoft]
  .MAG  MPS Magro Paint System Graphic
        MS Access Diagram Shortcut [Buy Office XP at Shop.Microsoft]
        MAGIchan Graphic  [XnView]
  .MAI  VAX Mail
  .MAK  Make File (compiler project file)
  .MAM  MS Access Macro Shortcut [Buy Office XP at Shop.Microsoft]
  .MAN  Manual (often an ASCII text file)
        Windows 2000 Mandatory User Profile (C:/DOCUMENTS AND SETTINGS/USERNAME/NTUSER.MAN)
  .MANIFEST  MS Visual Stylesheet for Windows Forms (Text file)
  .MAP  Image
        Server-side Image Map (allows one to map link locations in a Web graphic)
        Color Palette
        AccView Network Map
        Atlas MapMaker Map
        DIV Game Studio Map  [XnView]
        Fenix Map  [XnView]
        Ingres Termcap Mapping File
        Poser 3D Map File
        WorldCraft Quake/Half-Life Game Level File
        Blood Game File Map
        Duke Nukem Game Level Data File
          ...and many more games (too many to list)
        Linker Map
        Micrografx Picture Publisher Format Data
        PROGNOSIS Map Document File
  .MAPIMAIL  MS Outlook Express Mail File
  .MAQ  MS Access Query Shortcut [Buy Office XP at Shop.Microsoft]
  .MAR  MS Access Report Shortcut [Buy Office XP at Shop.Microsoft]
        VAX Macro Assembly Program
        Bibliographic Data Format (usually .MRC)
  .MAS  Focus Master Data Definition
        MS Access Stored Procedures [Buy Office XP at Shop.Microsoft]
        Lotus Freelance Graphics Smartmaster File
        QuickCard File
  .MAT  Sound File
        Pro/Engineer Material Properties File
        Matlab Variables Binary File
        MS Access Table Shortcut [Buy Office XP at Shop.Microsoft]
        Autodesk 3D Studio Max and Viz File
        Poser 3D Pose File
  .MAUD  Sound File [Linux Player]
  .MAV  MS Access View Shortcut [Buy Office XP at Shop.Microsoft]
  .MAW  MS Access Data Access Page
  .MAX  Kinetix's 3D Studio MAX Scene
        Autodesk 3ds Max Scene File
        Maximizer Contact & E-business Program
        Paperport Scanned Image [Viewer]
        Max Source Code
        OrCAD Layout File
  .MAZ  Hover Maze Data
        Division's dVS/dVISE File
  .MB   Paradox Memo Holder
        Maya Binary (3D Software Maya Scenes)
  .MB1  Apogee Monster Bash Data File
  .MBD  Multimedia Builder MP3 Authoring File
  .MBF  MS Money Backup File
  .MBFS  Stardent AVS X Image  [XnView]
  .MBFAVS  Stardent AVS X Image  [XnView]
  .MBG  Mailbag Assistant E-mail Archive
  .MBK  dBase IV Multiple Index Backup
        VersaPro Motion Block Backup
  .MBM  SymbianOS Multi BitMap Image (native EPOC image format)  [XnView]
  .MBS  Mailbag Assistant Script
  .MBT  ecBuilder Template (Web site cataloging)
  .MBW  MarketBrowser (investment charting/analysis)
  .MBX  Mailbox Message File (Outlook v1-4 or Eudora and others)
  .MC   MetaCard Script
        PlaySaver and PSEmuPro Memory Card Save and Single Game Save
  .MC8  Mastercam 8 File
  .MCA  i-deas Web ACCESS File
  .MCC  Mathcad Configuration
        Mylar City Character Editor
        Dialer10 Calling Card
        Monu-Cad Pro CAD File
        VectorWorks/MiniCAD File [Viewer]
        Incite Media Assistant File
  .MCD  Mathcad Document
        Craig McDowall.com NotePad
        Monu-Cad Pro CAD File
        Bleem! Memory Card Save
  .MCF  Mathcad Font
        Meta Content Format File (describes a Web site) [Process description]
        Master Command File
        TMPGEnc Template (Multimedia Container Format File)
  .MCH  Macromedia Xtra Cache File
  .MCI  Media Control Interface Command Set
  .MCL  Multimedia Manager Collection File
        Macro Command Language (Symbol handheld terminals)
  .MCP  Mathcad Printer Driver
        Capsule Application Script
  .MCQ  McAfee Quarantined File
  .MCR  DataCAD Keyboard Macro File
        PlaySaver and PSEmuPro Memory Card Save and Single Game Save
        CuteFTP Script
  .MCS  MathCAD Format File
  .MCT  Musicator
  .MCW  MacWrite II Macintosh Text File
  .MCX  Graphic File
  .MD   Compressed Archive File
        Teknical eLearning Objects Meta-Data File (stores info on related file)
  .MD1  Gear CD Suite File
  .MD5  MD5summer (generates and verifies md5 checksums) [MD5 Generator] [fsum Checksum Utility]
  .MDA  MS Access Add-in
        MS Access 2 Workgroup
  .MDB  MS Access Database
        MS Access Application
        Mediator Multimedia Data
  .MDE  MS Access Database File
  .MDF  Menu Definition File
        MS-SQL Master Database File
        Accelio Capture Classic (JetForm) Filler (JetForm Corp became Accelio 12 Sep 2001)
        I-deas Master Drafting Machine Data File
  .MDL  Digitrakker Music Module (by n-FaCToR)
        Rational Rose
        Quake Model File
        3D Design Plus Model
        Simulink Simulation Model
        ASTi Model Builder File
        CA-Compete! Spreadsheet
        Half-life Model  [XnView]
        Moray Model (wireframe modeller supporting POV-Ray 3.1)
        Symbian OS MIME Type Library
  .MDM  Telix Modem Definition
  .MDMP  WinXP Trouble Report (extension is added to file sent)
  .MDN  MS Access Blank Database Template [Buy Office XP at Shop.Microsoft]
  .MDO  MS Internet Information Server Configuration Backup
  .MDP  MS Developer Studio Project
  .MDR  FaxTalk Modem Doctor Modem Report File
  .MDS  Media Description File [Fantom CD Emulator]
  .MDT  MS Access Add-in Data [Buy Office XP at Shop.Microsoft]
        MS ILink Incremental Linker Data Table
  .MDW  MS Access Workgroup Information [Buy Office XP at Shop.Microsoft]
  .MDX  dBase IV Multiple Index [File Structure]
        Avery Label Pro Re-Index File
  .MDZ  MS Access Wizard Template [Buy Office XP at Shop.Microsoft]
  .ME   Information (e.g., READ.ME)
  .MEA  Meazure File (screen measurement and capture utility)
  .MEB  WordPerfect Macro Editor Bottom Overflow File
  .MED  WordPerfect Macro Editor Delete Save
        OctaMED Tracker Module
  .MEL  Ericsson Phone Melody
        Maya Embedded Language Script
  .MEM  WordPerfect Macro Editor Macro
        Memory File of Variables
        MS FoxPro Memory Variable Save File
  .MEN  Menu
  .MEQ  WordPerfect Macro Editor Print Queue
  .MER  WordPerfect Macro Editor Resident Area
        Data Interchange Format
  .MES  Message File
        WordPerfect Macro Editor Work Space
  .MET  WordPerfect Macro Editor Top Overflow File
        Presentation Manager Meta File
        OmniPage Document
        eDonkey2000 File
  .METHODS  Likely a text file (e.g., README.METHODS)
  .MEU  DOS Shell Menus
  .MEX  Matlab Executable Command
        WordPerfect Macro Editor Expound File
        mexReader Multimedia File
  .MEZ  RealArcade Game Information
  .MF   MetaFont Text File
  .MFA  MS Site Server 3.0 Report Definition
  .MFF  MIDI File Format
  .MFG  MediaForge Runtime Player
  .MFM  VTeX Multiple Master Font Metrics (a variant of the Adobe Font Metrics (AFM) format?)
  .MGC  MGCSoft Equation Editor File
  .MGCF  MagicInstall Compressed File
  .MGD  Master Grade Gradebook
  .MGF  Image File
        Micrografx Font
        Materials and Geometry Format File
  .MGL  MosASCII Graphics Library
  .MGM  MGCSoft Equation Editor Macro File
  .MGR  MGR Bitmap  [XnView]
  .MGX  Micrografx Picture Publisher Clipart
  .MGZ  Metal Gear Solid Archive  [Dragon UnPACKer]
  .MH   Graphic File
  .MHG  Multimedia File
  .MHK  Riven Movie Data File (Mohawk Archive)
  .MHP  MS Home Publishing Project
  .MHT  MS MHTML Document (Archived Web Page)
  .MHTML  MS MHTML Document (Archived Web Page)
  .MI   Miscellaneous
        CoCreate CAD File
  .MIB  Management Information Base File (SNMP Management Programs)
  .MIC  MS Image Composer File
  .MID  MIDI File  [IrfanView]
  .MIDI  MIDI File  [IrfanView]
  .MIF  MIDI Instrument
        Adobe FrameMaker Interchange Format
        Software License Tracking Tool (CERTAUTH.MIF)
        MapInfo Interchange Format File
        MicroHof .MIF Assembler File
        Image Magick File  [XnView]
  .MIFF  Image Magick File  [XnView]
  .MII  MicroStat II Data File
  .MIL  Group 4 Fax File
        Micro Illustrator Uncompressed Graphic  [XnView]
  .MIM  Multi-Purpose Internet Mail Extensions (MIME) File  [MIME]
  .MIO  mexReader Multimedia File
  .MIP  Paint Shop Pro Multiple Image Print File
  .MIS  Delta Force Land Warrior Mission [Fan site]
        Tribes 2 Game File
        MagicInstall Installation Script  (Under development Feb 2002)
  .MIX  Power C Object File
        Multilayer Picture File (MS PhotoDraw 2000 & MS Picture It!)
        Don Knuth's MIX Emulator
        Command & Conquer Movie/Sound File
        Techno eJay Music Mix File
        OzWin CompuServe E-mail/Forum Access Index File
  .MJ   MovieJack DVD Ripper File
  .MK   Make File
  .MKD  Malz++Kassner CAD5 Drawing
  .MKE  Make File
  .MKI  Picture File
  .MKL  Malz++Kassner CAD5 Drawing Library
  .MKS  Tact Data
  .ML3  Milestones 3.x Project
  .ML6  PowerPoint Milestone File
  .MLB  Macro Library
  .MLD  Multilizer Dictionary
  .MLI  Encyclopedia Media List
        3D Studio's Material-Library File
  .MLK  Sierra Mastercook File
  .MLM  Novel Groupwise E-mail File
  .MLS  Miles Sound Tools Compressed DLS
  .MM   Macro Mania Macro
        Multimate Advantage File
        Lightscape Material Map
  .MMB  MultiMedia Builder
        Oracle Forms Menu Binary Source Code
  .MMC  Media Catalog
        MSoffice Media Content (MS OfficeXP)
  .MME  Multi-Purpose Internet Mail Extensions (MIME) File  [MIME]
  .MMF  Meal Master Format
        MS Mail File
  .MMI  Memo Open Client
  .MML  Mail Meta Language
  .MMM  Animation MS Multimedia Movie
        MacroMind Directory RIFF/RMMP Format Movie
  .MMO  RapidFile Memo Writer
  .MMP  MindManager Map File
        Gammadyne Mailer Project File
        Bravado Board Video Output Format
  .MMPBT  MindManager Branch Template File
  .MMPT  MindManager Template
  .MMS  Miles Sound Tools (Midi+DLS/MLS)
  .MMSCRIPT  MindManager Script File
  .MMT  Nimbus 7 SAMS Data File (monthly mean retrieved temperatures)
  .MMV  Sony MovieShaker File
  .MMW  Microsoft Media Content
  .MMX  Command & Conquer Red Alert 2 Map File
        Oracle Forms Compiled Menu
  .MMZ  MusicMatch Theme File
  .MN2  Descent2 Mission File
  .MN3  Descent3 Mission File
  .MN4  Microsoft Money Database (older version)
  .MNB  MuPAD File
  .MNC  My Notes Center File
  .MND  AutoCAD Menu Program File
        MNI Mandelbrot for Windows
  .MNG  Animation Shop Animation
        DeLorme Map'n'Go Map
        Multi-image Network Graphic  [XnView]
  .MNO  Monopoly Saved Game
        Macromedia Design Notes
  .MNR  AutoCAD Compiled Menu File
  .MNS  AutoCAD ASCII Menu File
  .MNT  Foxpro Menu Memo
  .MNU  Menu File (various)
        HP NewWave Advanced Macro
  .MNW  Menu File (various)
  .MNX  AutoCAD Compiled Menu File
        Foxpro Menu
  .MNY  MS Money File
  .MOB  Device Definitions
  .MOD  Music File (various)
        Model File (various)
        Modula-2 Program File
        ProModel Optimization Software Suite Model
        Windows Kernel Module
        Amiga and PC Tracker Module
        MS Multiplan Spreadsheet
        Monarch File (data mining)
  .MODEL  Catia File
  .MOL  MDL Molfile (MIME type chemical/x-mdl-molfile) [Requires Chime Plug-in]
        Easy Palette Object Library
  .MON  ReadMail Monitor (UNIX)
  .MOP  Mopac Input File (MIME type chemical/x-mopac-input)
  .MOR  Poser 3D Morph Target File
  .MOV  QuickTime Video Clip  [IrfanView]
        Apple QuickTime Audio
        AutoCAD AutoFlix Movie
  .MOVERADDIN     Mover (Inventory Management) Add-in
  .MOVERBACKUP    Mover (Inventory Management) Backup Set
  .MOVERCONFIG    Mover (Inventory Management) Configuration
  .MOVERDB        Mover (Inventory Management) Database
  .MOVERREG       Mover (Inventory Management) Registration Info
  .MOVERTEMPLATE  Mover (Inventory Management) Template
  .MOVIE  Video
  .MOX  Extend Simulation Model File
  .MOZ  Netscape Temp File
  .MP   Multiplan File
        Maya Personal Learning Edition File
        EARS Component File (EARS = UK Liberal Democrats Election Agents Record System) [Filename starts with E]
  .MP+  MpegPlus Audio File (replaced by .MPC)
  .MP1  MPEG Audio Stream, Layer I
  .MP2  MPEG Audio Stream, Layer II
  .MP2V  MPEG Audio Stream, Layer II
  .MP3  MPEG Audio Stream, Layer III  [IrfanView]
        SHARP MZ-series Emulator File
  .MP4  iVAST MPEG-4 (hold BIFS-Binary Information For Scene representation) [MPEG-4 Industry Forum]
  .MPA  MPEG Audio Stream, Layer I, II or III
        Palm Memo File
  .MPC  MS Project Calender
        MP3 Collector Collection Manager File
        VersaPro Compiled Motion Block
        Musepack Audio File (new format replacing .MP+)
  .MPD  Mini Port Driver
        MS Project Database File
  .MPDEX  MPdex MP3 Database Utility
  .MPE  MPEG Movie Clip
  .MPE.EXE  MP3 Digital Player Wrapper
  .MPEG  MPEG Movie
  .MPF  MS Design Gallery
        MosASCII Project Workspace File
  .MPG  MPEG Animation  [IrfanView]
        MPEG 1 System Stream
  .MPGA  Mpeg-1 Layer3 Audio Stream
  .MPH  MS Publisher
  .MPJ  RoboHTML Project
        Mountain Video Editing File  (Atari)
  .MPK  Augmented MS-Project File
  .MPM  WordPerfect MathPlan Macro
        Max Payne MOD Archive [Added Info]
  .MPNT  MacPaint Bitmap File  [XnView]
  .MPO  Augmented MS-Project File
  .MPP  MS Project File
        CAD Drawing File
  .MPQ  Blizzard Game Data File
          (also other games)
  .MPR  Foxpro Program
        Westwood Studios Game File (e.g., Red Alert, et.al. - should be a text file)
        FileMaker Spelling Dictionary
  .MPS  Multimedia File
        MPEG-1 Audio and Video File (system stream)
        Casio PDL Pocket Streets Map (Microsoft product - see just below)
        MS Pocket Streets Map File
        Max Payne Saved Game
        Garmin Mapsource GPS Mapping Interface
        MySweetNix! (change MSN Messenger Service nickname every n seconds)
  .MPT  MS Project Template File
        Multipage TIFF Bitmap
  .MPV  MS Project View
        MPEG-1 Video File
  .MPV2  MPEG Audio Stream, Layer II
  .MPW  MosASCII Project Workspace File
  .MPX  Foxpro Compiler Menu
        MS Project Export File
        RCA/Lyra Handheld MP3 Player File (secure MP3 format that only plays in this player)
  .MRB  MS C++ Multiple Resolution Bitmap Graphic
  .MRC  MIRC Script File
        Bibliographic Data Format
  .MRF  Marks Russel File  [XnView]
  .MRI  MRI Scan
  .MRK  Informative Graphics Markup File
  .MRO  SharpEye Music Reader File
  .MRS  WordPerfect Macro Resource File
  .MRW  Minolta Diamage RAW Graphic (use view software supplied with camera)
  .MS   Checksum File for Anti-Virus
  .MS1  OzWin CompuServe E-mail/Forum Access Message File
  .MS3D  MilkShape 3D Model
  .MSA  Magic Shadow Archive
  .MSC  Microsoft Common Console Document
        MS C Makefile
  .MSF  Multiple Sequence File  (biomedical analysis)
  .MSG  Program Message
        OzWin CompuServe E-mail/Forum Access Message File
        MS Mail Message
  .MSH  MASH (The Microsoft Agent Scripting Helper)
  .MSI  Windows Installer File (associates components with features and contains installation control info)
  .MSK  Autodesk Mask File
        PaintShop Pro Mask File  [XnView]
  .MSM  MultiSIM Circuit Diagram
  .MSN  MS Network Document (possibly nicknames)
        Descent Mission File
  .MSO  MS Word OLE Web Page Storage Stream [Buy Office XP at Shop.Microsoft]
        MS FrontPage File [Buy Office XP at Shop.Microsoft]
        Math Script Object File
  .MSP  MS Paint Graphic File  [XnView]
        Windows Installer Patch
        Magix Music Studio File
  .MSPX  Related to Microsoft's .NET (still researching)
  .MSR  OzWin CompuServe E-mail/Forum Access SYSOP File
  .MSRCINCIDENT  MS Remote Assistance Request
  .MSS  Manuscript Text File (various)
        Game Score
  .MSSYTLES  Windows Visual Style File
  .MST  Minispecification
        DATAIR Pension System Master File
        Windows SDK Setup Transform Script (contains mods to apply to package during installation)
        ChemFinder Chemical Structure Index
        Visual Test Source File
  .MSW  Word Text File [Buy Office XP at Shop.Microsoft]
  .MSWMM  Microsoft Windows Movie Maker Project (Part of WinME & XP)
  .MSV  Sony Memory Stick Format
  .MSW  MS Word Text File
  .MSX  Compressed CP/M File Archive
  .MTA  MS Flight Simulator Maintenance File
  .MTB  MINITAB Exec File (a macro file)
  .MTD  Digital Sheet Music [Viewer]
  .MTF  Darkstone Archive  [Dragon UnPACKer]
        MicroSurfer File (Link manager/accelerator)
  .MTH  Derive Math File
  .MTK  Matrikon Software License File
  .MTL  MathLook File
  .MTM  Sound File
        MultiTracker Music Module
  .MTP  L&H Power Translator Pro
  .MTV  MTV Ray-tracer  [XnView]
  .MTW  Minitab Data File
  .MTX  Temporary File often used by a browser or TWAIN device
  .MU   Quattro Menu
  .MUC  Music Collector Collection Manager File
  .MUF  ProtoMuck Multi User Forth Program
  .MUL  Ultima Online Game
  .MUP  Music Publisher File
  .MUS  MusicTime Audio File
        Finale Music Score
        Harmony Assistant, Melody Assistant, Myriad Music plug-in, Melody Player
  .MV   Miva Script
  .MV3  Oozic 3D MusicVideo
  .MVA  Matrox Video Card Driver
  .MVB  Database
        MS Multimedia Viewer File  [Viewer Download]
          Note: The viewer download is old. Don't overwrite any new files with old.
  .MVC  Music Collector Collection Manager File
  .MVD  MicroDVD DVD Movie
  .MVE  Interplay Video File [Descent2]
  .MVF  Movie Stop Frame File
  .MVI  AutoCAD Movie Command File
  .MVW  Saber LAN Log File
  .MW4  MechWarrior 4 Map
  .MWD  Photo Soap2 File
  .MWF  ProMotion Animation
        Autodesk MapGuide Author Map Window File
  .MWM  Mail Warrior File
  .MWP  Lotus Wordpro 97 Smartmaster File
        MegaWorks Pack File  [Dutch]
  .MWS  Maple Spreadsheet
  .MWV  MovieWorks File
  .MX3  Bitbop Tuner Locked Sound File
  .MXD  GIS Project File (map information)
  .MXE  Macro Express
        Mindex Effect Album
  .MXI  Proteus File (personal light and sound stimulation system)
        Macromedia Extension Information
        Mindex Indices file for Indexed Images
  .MXM  MS Project/Outlook Team Assign Task
        Mindex Master Index File for a Category
  .MXP  Macromedia Extension Manager
        ArcReader Published Map
  .MXT  MS C
        ArcMap Map Template
  .MYD  MySQL Data File
  .MYI  MySQL Data File
  .MYDOCS  MyDocs Drop Target
  .MYP  Make Your Point Presentation
  .MYS  Myst Saved Game
  .MYW  MyWorld Education Drawing
  .MZ   MOZART Music Document
  .MZB  MegaZeux Board
  .MZF  SHARP MZ-series Emulator File
  .MZP  MOZART Percussion File
  .MZQ  SHARP MZ-series Emulator QuickDisk File
  .MZS  SHARP MZ-series Emulator File
  .MZT  MOZART Template File
        SHARP MZ-series Emulator File
  .MZX  MegaZeux World