| .LTX | GSC Game World | Arquivos de dados | S.T.A.L.K.E.R. Properties File | GSC Game World S.T.A.L.K.E.R.: Call of Pripyat | GSC Game World |
| .LUAR | UltraDefrag Development Team | Arquivos de dados | UltraDefrag Lua Report | UltraDefrag | UltraDefrag Development Team |
| .LUB | Interscape | Arquivos de dados | Lua Bytecode | LUA | Interscape |
| .LUCIDCOLORSET | The Escapers | Arquivos de dados | Lucid Color Set File | Lucid | The Escapers |
| .LUCY | HTC | Arquivos de dados | HTC Scribble Note | HTC Scribble | HTC |
| .LUD | ABBYY | Arquivos de dados | Lingvo User Dictionary File | ABBYY Lingvo Dictionary | ABBYY |
| .LUM | Kevin Chong | Arquivos de dados | Luminous Song List | Luminous | Kevin Chong |
| .LUT | Lutron Electronics Co., Inc | Arquivos de dados | RadioRA Essentials Project Database | Lutron Electronics RadioRA Essentials | Lutron Electronics Co., Inc |
| .LVM | National Instruments | Arquivos de dados | LabVIEW Measurement File | LabVIEW | National Instruments |
| .LVS | Daylon Graphics | Arquivos de dados | Daylon Leveller Selection Mask File | Daylon Leveller | Daylon Graphics |
| .LVW | New Wave Concepts | Arquivos de dados | Livewire Document | LiveWire | New Wave Concepts |
| .LW | NewTek | Arquivos de dados | LightWave 3D Binary File | LightWave 3D | NewTek |
| .LW2 | Johm Mackernon Software | Arquivos de dados | Lightwright Version 2 Show Data File | LightWright | Johm Mackernon Software |
| .LW4 | Johm Mackernon Software | Arquivos de dados | Lightwright File | LightWright | Johm Mackernon Software |
| .LW5 | Johm Mackernon Software | Arquivos de dados | Lightwright File | LightWright | Johm Mackernon Software |
| .LWD | EditShare | Arquivos de dados | Lightworks Data File | Lightworks | EditShare |
| .LWO | NewTek | Arquivos de dados | LightWave 3D Object File | Poser | Smith Micro Software |
| .LWP | IBM | Arquivos de dados | Lotus Word Pro Document | IBM Lotus Word Pro | IBM |
| .LWR | Atari Corporation | Arquivos de dados | RollerCoaster Tycoon Laser Writing File | RollerCoaster Tycoon | Chris Sawyer |
| .LXE | Foundry | Arquivos de dados | Luxology Modo Environment Preset | Modo | Foundry |
| .LXF | The LEGO Group | Arquivos de dados | LEGO Digital Designer Model File | LEGO Digital Designer | The LEGO Group |
| .LXK | Open Source | Arquivos de dados | Lexicon Link-up File | COREX | Open Source |
| .LY | GNU Operating System | Arquivos de dados | LilyPond File | LilyPond | GNU Project |
| .LYC | SPGPrints Group | Arquivos de dados | BestIMAGE Compressed Design File | spgprints bestIMAGE | SPGPrints Group |
| .LYT | Adminsoft | Arquivos de dados | Adminsoft Document Layout File | Adminsoft | Adminsoft |
| .LYX | Open Source | Arquivos de dados | XWE File | XWE | Open Source |
| .LZZZZZZZ | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .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 |
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