M

File extensions starting with the letter M...

  .M    Matlab Function
        Macro Source
        Mathematica File
  .M    Limbo Interface Declaration (Inferno OS)
  .M??  Ingres Modify Table/Index File (?? = Hex 00 to FF)
  .M18  Accolade Golf Course File
  .M1V  MPEG File
  .M2V  MPEG-2 File
  .M3   ModuleA 3 Program File
  .M3A  MPEG Archive Enhanced .M3U Playlist File
  .M3D  3D Animations Macro
        Corel Motion 3D Animation
  .M3U  MPEG URL
  .MA3  Harvard Macro (Harvard Graphics taken over by Serif)
  .MAC  MacPaint Bitmap Graphic
        Macro (various)
  .MAD  MS Access Module Shortcut
  .MAF  MS Access Form Shortcut
  .MAG  Picture File
        MS Access Diagram Shortcut
  .MAI  Mail
  .MAK  Make File (compiler project file)
  .MAM  MS Access Macro Shortcut
  .MAN  Manual
  .MAP  Image
        Color Palette
        Duke Nukem WAD File
        Ingres Termcap Mapping File
        Linker Map
        Micrografx Picture Publisher Format Data
  .MAQ  MS Access Query Shortcut
  .MAR  MS Access Report Shortcut
  .MAS  Focus Master Data Definition
        MS Access Stored Procedures
        Lotus Freelance Graphics Smartmaster File
  .MAT  Sound File
        Pro/Engineer Material Properties File
        Matlab Variables Binary File
        MS Access Table Shortcut
        Autodesk 3D Studio Max and Viz File
  .MAV  MS Access View Shortcut
  .MAW  MS Access Data Access Page
  .MAX  Kinetix's 3D Studio MAX Scene
        Paperport Scanned Image
        OrCAD Layout File
  .MAZ  Hover Maze Data
        Division's dVS/dVISE File
  .MB   Paradox Memo Holder
  .MB1  Apogee Monster Bash Data File
  .MBF  MS Money Backup File
  .MBK  dBase IV Multiple Index Backup
  .MBX  Mailbox Message File (Outlook v1-4 or Eudora)
  .MCC  Mathcad Configuration
        Dialer10 Calling Card
        Monu-Cad Pro CAD File
  .MCD  Mathcad Document
        Monu-Cad Pro CAD File
  .MCF  Mathcad Font
  .MCI  Media Control Interface Command Set
  .MCL  Multimedia Manager Collection File
  .MCP  Mathcad Printer Driver
  .MCR  DataCAD Keyboard Macro File
  .MCS  MathCAD Format File
  .MCW  Word for Macintosh Text File
  .MCX  Graphic File
  .MD   Compressed Archive File 
  .MDA  MS Access Add-in
        MS Access 2 Workgroup
  .MDB  MS Access Database
        MS Access Application
  .MDE  MS Access Database File
  .MDF  Menu Definition File
  .MDL  Digitrakker Music Module (by n-FaCToR)
        Rational Rose
        Quake Model File
  .MDM  Telix Modem Definition
  .MDN  MS Access Blank Database Template
  .MDP  MS Developer Studio Project
  .MDT  MS Access Add-in Data
  .MDW  MS Access Workgroup Information
  .MDX  dBase IV Multiple Index
  .MDZ  MS Access Wizard Template
  .ME   Information (e.g., READ.ME)
  .MEB  WordPerfect Macro Editor Bottom Overflow File
  .MED  WordPerfect Macro Editor Delete Save
        OctaMED Tracker Module
  .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
  .MEU  DOS Shell Menus
  .MEX  Matlab Executable Command
        WordPerfect Macro Editor Expound File
  .MEZ  RealArcade Game Information
  .MF   MetaFont Text File
  .MFF  MIDI File Format
  .MGC  MGCSoft Equation Editor File
  .MGF  Image File
        Micrografx Font
        Materials and Geometry Format File
  .MGM  MGCSoft Equation Editor Macro File
  .MH   Graphic File
  .MHG  Multimedia File
  .MHT  MS MHTML Document (Archived Web Page)
  .MI   Miscellaneous
  .MIB  Management Information Base File (SNMP Management Programs)
  .MIC  MS Image Composer File
  .MID  MIDI File  [Viewer]
  .MIF  MIDI Instrument
        Adobe FrameMaker Interchange Format
  .MIL  Group 4 Fax File
  .MIM  Multi-Purpose Internet Mail Extensions (MIME) File  [MIME]
  .MIX  Power C Object File
        Multilayer Picture File (MS PhotoDraw 2000 & MS Picture It!)
        Command & Conquer Movie/Sound File
        Techno eJay Music Mix File
  .MK   Make File
  .MKE  Make File
  .MKI  Picture File  
  .MLB  Macro Library  
  .MLI  Encyclopedia Media List
        3D Studio's Material-Library File
  .MLS  Miles Sound Tools Compressed DLS
  .MM   Macro Mania Macro
        Lightscape Material Map
  .MMB  MultiMedia Builder
  .MMC  Media Catalog  
  .MME  Multi-Purpose Internet Mail Extensions (MIME) File  [MIME]
  .MMF  Meal Master Format
        MS Mail File
  .MML  Mail Meta Language
  .MMM  Animation MS Multimedia Movie
  .MMP  MindManager Player Play List File
  .MMS  Miles Sound Tools (Midi+DLS/MLS)
  .MMZ  MusicMatch Theme File
  .MN2  Descent2 Mission File
  .MN3  Descent3 Mission File
  .MND  AutoCAD Menu Program File
        MNI Mandelbrot for Windows
  .MNG  Animation Shop Animation
        Multi-image Network Graphic
  .MNT  Foxpro Menu Memo
  .MNU  Menu File (various)
  .MNW  Menu File (various)
  .MNX  AutoCAD Compiled Menu File
        Foxpro Menu
  .MNY  MS Money File
  .MOB  Device Definitions  
  .MOD  Music File
        ModuleA-2 Program File
        Windows Kernel Module
        Amiga and PC Tracker Module
        MS Multiplan Spreadsheet
  .MODEL  Catia File
  .MOV  QuickTime Video Clip  [Viewer]
        Apple QuickTime Audio
  .MOZ  Netscape Temp File
  .MP   Multiplan File
  .MP1  MPEG Audio Stream, Layer I
  .MP2  MPEG Audio Stream, Layer II
  .MP3  MPEG Audio Stream, Layer III  [Viewer]
  .MPA  MPEG Audio Stream, Layer I, II or III
  .MPC  MS Project Calender
  .MPD  Mini Port Driver
        MS Project Database File
  .MPE  MPEG Movie Clip
  .MPE.EXE  MP3 Digital Player Wrapper
  .MPEG  MPEG Movie
  .MPG  MPEG Animation  [Viewer]
        MPEG 1 System Stream
  .MPJ  RoboHTML Project
  .MPM  WordPerfect MathPlan Macro
  .MPP  MS Project File
        CAD Drawing File
  .MPQ  Blizzard Game Data File
  .MPR  Foxpro Program
  .MPS  Multimedia File
  .MPT  MS Project Template File
  .MPV  MS Project View
  .MPX  Foxpro Compiler Menu
        MS Project Export File
  .MRB  Multiple Resolution Bitmap Graphic
  .MRC  MIRC Script File
  .MRI  MRI Scan
  .MRK  Informative Graphics Markup File
  .MRS  WordPerfect Macro Resource File
  .MS   Checksum File for Anti-Virus
  .MSA  Magic Shadow Archive
  .MSC  Microsoft Common Console Document
  .MSG  Program Message
        OzWin Message/Mail File
        MS Mail Message
  .MSH  MASH (The Microsoft Agent Scripting Helper)
  .MSI  Windows Installer File
  .MSK  Autodesk Mask File
        PaintShop Pro Mask File
  .MSN  MS Network Document
        Descent Mission File
  .MSP  MS Paint Graphic File
        Windows Installer Patch
  .MST  Minispecification  
        DATAIR Pension System Master File
        Windows SDK Setup Script
        Visual Test Source File
  .MSW  Word Text File
  .MSV  Sony Memory Stick Format
  .MTH  Derive Math File
  .MTK  Matrikon Software License File
  .MTM  Sound File
        MultiTracker Music Module
  .MTV  Picture File
  .MTW  Minitab Data File
  .MU   Quattro Menu
  .MUL  Ultima Online Game
  .MUP  Music Publisher File
  .MUS  Audio File
  .MVB  Database
        MS Multimedia Viewer File
  .MVE  Interplay Video File [Descent2]
  .MVF  Movie Stop Frame File  
  .MWP  Lotus Wordpro 97 Smartmaster File
        MegaWorks Pack File  [Dutch]
  .MXT  MS C
  .MYS  Myst Saved Game
  .MZ   MOZART Music Document
  .MZT  MOZART Template File