| .M | MathWorks | Arquivos de dados | MATLAB Source Code File | Notepad++ | Don Ho |
| .M11 | Microsoft Corporation | Arquivos de dados | Microsoft Money 2003 Data | Microsoft Money | Microsoft Corporation |
| .M2C | IBM | Arquivos de dados | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .M2O | Niklaus Wirth | Arquivos de dados | Modula Fitted Modula2 File | Modula | Niklaus Wirth |
| .M3I | IBM | Arquivos de dados | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .M3R | Autodesk, Inc. | Arquivos de dados | Autodesk Moldflow 3D Fill+Pack Restart Data | Moldflow Communicator | Autodesk, Inc. |
| .M4C | IBM | Arquivos de dados | IBM Voice Type Languages Newuser File | IBM Voice Type | IBM |
| .M4T | Sage | Arquivos de dados | Sage MAS 90 Data File | Sage MAS 90 | Sage |
| .MA | Autodesk, Inc. | Arquivos de dados | Maya Project File | Autodesk Maya | Autodesk, Inc. |
| .MA2 | Blizzard Entertainment Inc. | Arquivos de dados | Diablo II Map File | Diablo II | Blizzard Entertainment Inc. |
| .MAC2 | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MACRO | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MAF | National Cancer Institute | Arquivos de dados | Mutation Annotation Format File | Microsoft Notepad | Microsoft Corporation |
| .MAG | Microsoft Corporation | Arquivos de dados | Access Diagram Shortcut File | Microsoft Access | Microsoft Corporation |
| .MAI | Microsoft Corporation | Arquivos de dados | Microsoft Mail File | Microsoft Mail | Microsoft Corporation |
| .MAIL | NeoPlanet Inc | Arquivos de dados | NeoPlanet Mail Client File | NeoPlanet | NeoPlanet Inc |
| .MAILABVIEW | Microsoft Corporation | Arquivos de dados | MS AddressBook File | Microsoft Windows | Microsoft Corporation |
| .MAILBOX | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MAIN | FileMaker Inc. | Arquivos de dados | FileMaker Dictionary Data | FileMaker Pro | FileMaker Inc. |
| .MAJ | Autodesk, Inc. | Arquivos de dados | Camduct Job File | Autodesk Fabrication CAMduct | Autodesk, Inc. |
| .MAP | id Software | Arquivos de dados | Quake Engine Map File | Valve Hammer Editor | Valve |
| .MAPS | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MAR | Microsoft Corporation | Arquivos de dados | Microsoft Access Report | Microsoft Access | Microsoft Corporation |
| .MARCH | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .MARIO | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MAS | Image Space Incorporated | Arquivos de dados | rFactor Track File | Image Space rFactor | Image Space Incorporated |
| .MAT | MathWorks | Arquivos de dados | MATLAB MAT-File | The MathWorks MATLAB | MathWorks |
| .MB1 | Apogee Software, Ltd. | Arquivos de dados | Monster Bash Game Data File | Monster Bash | Apogee Software, Ltd. |
| .MBA | Benetech | Arquivos de dados | Martus Human Rights Bulletin System Data | Martus | Benetech |
| .MBB | Kodak | Arquivos de dados | Kodak EasyShare Data File | Kodak EasyShare | Kodak |
| .MBD | Mediachance | Arquivos de dados | Multimedia Builder Project File | MediaChance Multimedia Builder | Mediachance |
| .MBDB | Apple | Arquivos de dados | iTunes Backup Manifest Database | Apple iTunes | Apple |
| .MBL | Vernier Software & Technology | Arquivos de dados | Logger Pro Data File | Vernier Logger Pro | Vernier Software & Technology |
| .MBOX | Unknown Developer | Arquivos de dados | E-mail Mailbox | Mozilla Thunderbird | Mozilla |
| .MBP | Mobipocket | Arquivos de dados | Mobipocket Notes File | MBP reader | Angelfire |
| .MBSA | Microsoft Corporation | Arquivos de dados | Microsoft Baseline Security Analyzer File | Microsoft Baseline Security Analyzer | Microsoft Corporation |
| .MBT | Interscape | Arquivos de dados | Blue Card Manager Merit Badge Template File | Blue Card Manager | Scout Management Software |
| .MBW | Firesage Solutions | Arquivos de dados | MBRWizard Archive | Firesage Solutions MBRWizard | Firesage Solutions |
| .MBX | Microsoft Corporation | Arquivos de dados | Outlook Express Mailbox | Microsoft Outlook Express | Microsoft Corporation |
| .MC | Sendmail, Inc. | Arquivos de dados | Sendmail M4 Configuration | Sendmail | Proofpoint, Inc. |
| .MC1 | MedCalc Software | Arquivos de dados | MedCalc Data File | MedCalc | MedCalc Software |
| .MC4 | Cengage Learning | Arquivos de dados | MicroCase V4 Data File | MicroCase | Cengage Learning |
| .MCA | Mojang | Arquivos de dados | Minecraft "Anvil" Map File | Minecraft | Mojang |
| .MCB | NEPLAN AG | Arquivos de dados | NEPLAN Project | NEPLAN Electricity | NEPLAN AG |
| .MCD | Nemetschek Group | Arquivos de dados | MiniCAD Design File | Vectorworks Viewer | Vectorworks |
| .MCDX | PTC | Arquivos de dados | Mathcad Prime Document | Mathcad | PTC |
| .MCP | Freescale | Arquivos de dados | CodeWarrior Project | CodeWarrior | NXP |
| .MCQ | McAfee, Inc. | Arquivos de dados | MCQ McAfee Quarantined File | McAfee VirusScan | McAfee, Inc. |
| .MCT | Microsoft Corporation | Arquivos de dados | Windows Live Messenger Data File | 7-Zip | Igor Pavlov |
| .MCX | CNC Software | Arquivos de dados | Mastercam X And X2 File Format | Mastercam | CNC Software |
| .MD | Various Developers | Arquivos de dados | Markdown Documentation File | Microsoft Notepad | Microsoft Corporation |
| .MDB | Microsoft Corporation | Arquivos de dados | Microsoft Access Database | SAS | SAS Institute Inc. |
| .MDC | IBM | Arquivos de dados | Multi Dimension Cube File | Cognos software | IBM |
| .MDF | Alcohol Soft | Arquivos de dados | Alcohol 120% Disk Image File Format | IsoBuster | Smart Projects |
| .MDJ | MKLab | Arquivos de dados | StarUML Model File | MKLab StarUML | MKLab |
| .MDL | MathWorks | Arquivos de dados | MathWorks Simulink Model | Simulink | MathWorks |
| .MDM | Scientific Software International, Inc. | Arquivos de dados | HLM Multivariate Data Matrix File | SSI HLM software | Scientific Software International, Inc. |
| .MDT | Microsoft Corporation | Arquivos de dados | Microsoft Access Data File | Microsoft Access | Microsoft Corporation |
| .MDX | Disc Soft Ltd. | Arquivos de dados | Extended Media Descriptor File | DAEMON Tools | Disc Soft Ltd. |
| .MDZ | Microsoft Corporation | Arquivos de dados | Access Wizard Template | Microsoft Access | Microsoft Corporation |
| .ME | Unknown Developer | Arquivos de dados | Temporary Delete Me File | Unknown Software | Unknown Developer |
| .ME1 | Unknown Developer | Arquivos de dados | 21 Sample Winexam File | Unknown Software | Unknown Developer |
| .MEA | Malvern Instruments Ltd | Arquivos de dados | Mastersizer 2000 Sample Analysis Data | Mastersizer 2000 Software | Malvern Instruments Ltd |
| .MED | Rockwell Automation Inc. | Arquivos de dados | RSView Development Project Archive | Rockwell Automation RSView Studio or RSView ME | Rockwell Automation Inc. |
| .MEDLINE | National Library of Medicine | Arquivos de dados | MEDLINE Document | Microsoft Notepad | Microsoft Corporation |
| .MEG | Pennsylvania State University | Arquivos de dados | MEGA Data File | MEGA | Pennsylvania State University |
| .MEM | Microsoft Corporation | Arquivos de dados | FoxPro Variable File | Microsoft Visual FoxPro | Microsoft Corporation |
| .MEMORY | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MEN | CABRILOG | Arquivos de dados | GeometryII Plus Utility File | Geometry II Plus | CABRILOG |
| .MEQ | Corel | Arquivos de dados | Corel WordPerfect Macro Editor Print Queue File | Corel WordPerfect | Corel |
| .MER | Rockwell Automation Inc. | Arquivos de dados | RSView Development Runtime File | Rockwell Automation RSView Studio or RSView ME | Rockwell Automation Inc. |
| .MERLIN | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MES | Corel | Arquivos de dados | Corel WordPerfect Macro Editor Work Space Data | Corel WordPerfect | Corel |
| .MESA | OpenGL | Arquivos de dados | OpenGL GLUT File | GLUT | Silicon Graphics, Inc. |
| .MESSAGE | WebSTAR | Arquivos de dados | WebSTAR Directory Indexer Message | WebSTAR | Kerio Technologies |
| .MESSAGES | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MET | Emulex Corporation | Arquivos de dados | eMule Resource File | eMule | Open Source |
| .METAL | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MEU | Microsoft Corporation | Arquivos de dados | DOS Shell Menu Group File | MS-DOS | Microsoft Corporation |
| .MEX | MathWorks | Arquivos de dados | MATLAB Dynamically Linked Subroutine File | The MathWorks MATLAB | MathWorks |
| .MEZ | MusicEase Software | Arquivos de dados | MusicEase Document File | MusicEase | MusicEase Software |
| .MFA | Clickteam | Arquivos de dados | Multimedia Fusion Development File | Multimedia Fusion | Interscape |
| .MFD | Yamaha Corporation | Arquivos de dados | Music Finder Database | MusicFinderView | PSR Tutorial |
| .MFI | Microsoft Corporation | Arquivos de dados | Windows 98 Resource Kit Data Format | Microsoft Windows | Microsoft Corporation |
| .MFJ | Jarrold Group - Physical and Analytical Chemistry | Arquivos de dados | MOBCAL Data File | MOBCAL | Jarrold Group - Physical and Analytical Chemistry |
| .MFL | Verity Software House | Arquivos de dados | ModFit LT Analysis Report File | ModFit LT | Verity Software House |
| .MFO | Perl Express Group | Arquivos de dados | Perl ModInfo Descriptor File | Perl | Larry Wall |
| .MFR | Autodesk, Inc. | Arquivos de dados | Autodesk Moldflow Result Data | Moldflow Communicator | Autodesk, Inc. |
| .MFT | Kaspersky Lab | Arquivos de dados | Kaspersky File Table | Kaspersky Anti-Virus | Kaspersky Lab |
| .MFU | MobileFrame | Arquivos de dados | MobileFrame Update File | MobileFrame Desktop | MobileFrame |
| .MGC | Microsoft Corporation | Arquivos de dados | Microsoft Clip Organizer Media Catalog | Microsoft Office | Microsoft Corporation |
| .MGD | Maxium Developments Inc. | Arquivos de dados | Master Grade Gradebook | Master Grad | Maxium Developments Inc. |
| .MGP | Adobe Systems Incorporated | Arquivos de dados | Adobe Captivate MenuBuilder Data | Adobe Captivate | Adobe Systems Incorporated |
| .MGR | Unknown Developer | Arquivos de dados | MGR Bitmap | XnView MP | XnSoft |
| .MGW | Unknown Developer | Arquivos de dados | Microgateway Policy Implementation Data | Microgateway | Unknown Developer |
| .MHP | Open Source | Arquivos de dados | Maths Helper Plus File | Maths Helper Plus | Open Source |
| .MHX | Fujitsu Limited | Arquivos de dados | Fujitsu MicroController Firmware | Fujitsu microcontroller devices. | Fujitsu Limited |
| .MICE | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MIF | Adobe Systems Incorporated | Arquivos de dados | FrameMaker Interchange Format File | Adobe FrameMaker | Adobe Systems Incorporated |
| .MIO | Open Source | Arquivos de dados | MioEngine Application File | MioFactory | Open Source |
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