| .LDB | Microsoft Corporation | Fichiers de jeu | Microsoft Access Lock File | Microsoft Access | Microsoft Corporation |
| .LDW | LDW Software | Fichiers de jeu | Virtual Villagers Saved Game File | LDW Virtual Villagers | LDW Software |
| .LEC | LucasArts Entertainment Company, LLC | Fichiers de jeu | LucasArts Game Resource | Loom | LucasArts Entertainment Company, LLC |
| .LEV | Interscape | Fichiers de jeu | NetHack Level File | NetHack | Interscape |
| .LFD | LucasArts Entertainment Company, LLC | Fichiers de jeu | LucasArts Game Resource | Loom | LucasArts Entertainment Company, LLC |
| .LFL | LucasArts Entertainment Company, LLC | Fichiers de jeu | LucasArts Games Resource File | ScummVM | Interscape |
| .LFR | Marti wong | Fichiers de jeu | Little Fighter File | Little fighter | Marti wong |
| .LGL | Open Source | Fichiers de jeu | LeechGet Download List | LeechGet | Open Source |
| .LGP | Microsoft Corporation | Fichiers de jeu | Microsoft Windows Application Log File | Microsoft Windows | Microsoft Corporation |
| .LGT | Microsoft Corporation | Fichiers de jeu | Let's Go! Theme File | Let's Go! | Microsoft Corporation |
| .LIF | The LEGO Group | Fichiers de jeu | LEGO Digital Designer Assets File | LEGO Digital Designer | The LEGO Group |
| .LIP | CELSYS | Fichiers de jeu | Clip Studio Paint File | CELSYS Clip Studio Paint Pro | CELSYS |
| .LIT | Microsoft Corporation | Fichiers de jeu | Microsoft Reader eBook File | Calibre | Open Source |
| .LL | Combit | Fichiers de jeu | List & Label Preview File | List&Label | Combit |
| .LMP | id Software | Fichiers de jeu | Quake Engine Lump File | Doom | id Software |
| .LMU | ENTERBRAIN, INC. | Fichiers de jeu | RPG Maker Map File | RPG Maker VX | ENTERBRAIN, INC. |
| .LNC | Sports Interactive | Fichiers de jeu | Football Manager Player Data | Football Manager 2016 | Sports Interactive |
| .LNGP | 11 bit studios | Fichiers de jeu | This War Of Mine Language Localization Pack | This War Of Mine | 11 bit studios |
| .LNZ | Ubisoft | Fichiers de jeu | Petz Linez Data | Petz | Ubisoft Blue Byte |
| .LOC | TopoGrafix | Fichiers de jeu | GPS Location File | EasyGPS | TopoGrafix |
| .LOCK | Mozilla | Fichiers de jeu | Lock File | Mozilla Firefox | Mozilla |
| .LOD | Ubisoft | Fichiers de jeu | Homeworld Level Of Detail Data | Homeworld | Relic Entertainment |
| .LPR | Relic Entertainment | Fichiers de jeu | Homeworld File | Homeworld 2 | Sierra Entertainment |
| .LRF | Aequus Gaming LTD | Fichiers de jeu | League Of Legends Replay File | LOLReplay | Aequus Gaming LTD |
| .LRM | Microsoft Corporation | Fichiers de jeu | Encarta Class Server Learning Resource File | Microsoft Encarta | Microsoft Corporation |
| .LRT | Aequus Gaming LTD | Fichiers de jeu | League Of Legends Replay File | LOLReplay | Aequus Gaming LTD |
| .LSD | ENTERBRAIN, INC. | Fichiers de jeu | RPG Maker Game Save File | RPG Maker VX | ENTERBRAIN, INC. |
| .LSV | Light-O-Rama | Fichiers de jeu | Light-O-Rama Sequence Editor Visual Preference File | Light-O-Rama | Light-O-Rama |
| .LSW | Technics | Fichiers de jeu | Technics Keyboard Current Panel File | Unknown Software | Unknown Developer |
| .LSX | Microsoft Corporation | Fichiers de jeu | Streaming Media Shortcut | Microsoft Windows Media Player | Microsoft Corporation |
| .LTG | JEK Software | Fichiers de jeu | LaserTank Graphics File | LaserTank | JEK Software |
| .LTR | Sublime HQ Pty Ltd | Fichiers de jeu | Letter Document | Microsoft Notepad | Microsoft Corporation |
| .LTX | GSC Game World | Fichiers de jeu | 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 |
| .LUG | Unknown Developer | Fichiers de jeu | Game Data | Dragon UnPACKer | Open Source |
| .LUXB | Sillysoft Games | Fichiers de jeu | Lux Map File | Lux | Sillysoft Games |
| .LVB | LucasArts Entertainment Company, LLC | Fichiers de jeu | Outlaws Game File | Outlaws | LucasArts Entertainment Company, LLC |
| .LVL | Unknown Developer | Fichiers de jeu | Game Level File | Various video games | Various Developers |
| .LVZ | Open Source | Fichiers de jeu | Continuum Zone Data Graphics | Subspace Continuum | Open Source |
| .LZS | Open Source | Fichiers de jeu | LARC Compressed File Archive | ZipZag | Open Source |
| .M2 | Unknown Developer | Fichiers de jeu | PC-98 Game Music File | FMPMD2000 | Unknown Developer |
| .M3S | Ubisoft | Fichiers de jeu | Myst III Exile Saved Game | Myst III: Exile | Ubisoft |
| .M4S | Ubisoft | Fichiers de jeu | Myst IV: Revelation Save Game File | Myst IV: Revelation | Ubisoft |
| .M8 | Raven software | Fichiers de jeu | Heretic II MipMap Image File | Heretic II | Raven software |
| .M8M | SourceForge | Fichiers de jeu | 8mam8 Game Data File | 8mam8 | SourceForge |
| .MA | Autodesk, Inc. | Fichiers de jeu | Maya Project File | Autodesk Maya | Autodesk, Inc. |
| .MA2 | Blizzard Entertainment Inc. | Fichiers de jeu | Diablo II Map File | Diablo II | Blizzard Entertainment Inc. |
| .MAD | Electronic Arts | Fichiers de jeu | Electronic Arts Madcow Movie File | Media Player Classic | Open Source |
| .MAE | Interscape | Fichiers de jeu | My Avatar Editor Character File | My Avatar Editor | Interscape |
| .MAP | id Software | Fichiers de jeu | Quake Engine Map File | Valve Hammer Editor | Valve |
| .MAPLET | Blitz Research | Fichiers de jeu | Maplet World File | Blitz Research Maplet | Blitz Research |
| .MAS | Image Space Incorporated | Fichiers de jeu | rFactor Track File | Image Space rFactor | Image Space Incorporated |
| .MAX | Autodesk, Inc. | Fichiers de jeu | 3ds Max Scene File | Autodesk 3ds Max | Autodesk, Inc. |
| .MAZ | Microsoft Corporation | Fichiers de jeu | MAZ | Hover! | Microsoft Corporation |
| .MB1 | Apogee Software, Ltd. | Fichiers de jeu | Monster Bash Game Data File | Monster Bash | Apogee Software, Ltd. |
| .MCA | Mojang | Fichiers de jeu | Minecraft "Anvil" Map File | Minecraft | Mojang |
| .MCLEVEL | Mojang | Fichiers de jeu | Minecraft Map File | Minecraft | Mojang |
| .MCR | Mojang | Fichiers de jeu | Minecraft Region File | Minecraft | Mojang |
| .MCWORLD | Smith Micro Software | Fichiers de jeu | Minecraft World Backup File | 7-Zip | Igor Pavlov |
| .MD | Various Developers | Fichiers de jeu | Markdown Documentation File | Microsoft Notepad | Microsoft Corporation |
| .MD2 | Alcohol Soft | Fichiers de jeu | Alcohol Disk Image Segment 2 | Alcohol 120% | Alcohol Soft |
| .MD3 | id Software | Fichiers de jeu | Quake 3 3D Model | QuArK | QuArK Development Team |
| .MDL | MathWorks | Fichiers de jeu | MathWorks Simulink Model | Simulink | MathWorks |
| .MDM | Scientific Software International, Inc. | Fichiers de jeu | HLM Multivariate Data Matrix File | SSI HLM software | Scientific Software International, Inc. |
| .MEG | Pennsylvania State University | Fichiers de jeu | MEGA Data File | MEGA | Pennsylvania State University |
| .MEM | Microsoft Corporation | Fichiers de jeu | FoxPro Variable File | Microsoft Visual FoxPro | Microsoft Corporation |
| .MENU | id Software | Fichiers de jeu | Quake 3 Engine Menu File | Microsoft Notepad | Microsoft Corporation |
| .MF | Walt Disney Imagineering | Fichiers de jeu | Gameplay Multifile | Panda3D | Walt Disney Imagineering |
| .MGL | Microsoft Corporation | Fichiers de jeu | Age Of Empires 2 Replay File | Microsoft Age of Empires | Ensemble Studios |
| .MGX | Microsoft Corporation | Fichiers de jeu | Rise Of Nations Saved Game | Rise Of Nations | Big Huge Games |
| .MGZ | KONAMI | Fichiers de jeu | Metal Gear Solid Archive File | Metal Gear Solid | KONAMI |
| .MII | Nintendo | Fichiers de jeu | Wii Virtual Avatar File | My Avatar Editor | Interscape |
| .MINE | Mojang | Fichiers de jeu | Minecraft Map File | Minecraft | Mojang |
| .MIS | GarageGames | Fichiers de jeu | Marble Blast Gold Mission File | Delta Force | NovaLogic |
| .MIX | Microsoft Corporation | Fichiers de jeu | Microsoft Image Exchange File | Microsoft Picture It! | Microsoft Corporation |
| .MKR | Microsoft Corporation | Fichiers de jeu | Train Simulator Marker File | Microsoft Train Simulator | Kuju Entertainment |
| .MLX | MathWorks | Fichiers de jeu | MATLAB Live Script | The MathWorks MATLAB | MathWorks |
| .MM | Kodak | Fichiers de jeu | Kodak EasyShare Thumbnail Cache File | Kodak EasyShare | Kodak |
| .MMR | Fuji Xerox | Fichiers de jeu | Fuji Xerox Fax Image | FaxSee Pro | SFaxTools |
| .MMX | Interscape | Fichiers de jeu | Command And Conquer Game Data | Command and Conquer | Interscape |
| .MN2 | Interplay Entertainment | Fichiers de jeu | Descent 2 Mission File | Interplay Descent 2 | Interplay Entertainment |
| .MO | Dassault Systèmes | Fichiers de jeu | Dymola Simulation File | Dymola | Dassault Systèmes |
| .MOB | Microsoft Corporation | Fichiers de jeu | MOBTV Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MOD | Open Source | Fichiers de jeu | Amiga Music Module File | ModPlug Player | Open Source |
| .MON | Mozilla | Fichiers de jeu | Firefox Monday Bookmark Backup File | Mozilla Firefox | Mozilla |
| .MOR | Corel | Fichiers de jeu | Corel Shared Writing Tools Data | Corel Paradox | Corel |
| .MOS | MamiyaLeaf | Fichiers de jeu | Leaf Camera RAW File | MacPhun ColorStrokes | Macphun |
| .MP2 | New World Computing | Fichiers de jeu | Heroes Of Might And Magic II Map File | Heroes of Might & Magic III | Ubisoft |
| .MP2M | Rockstar Games | Fichiers de jeu | Max Payne 2 Mod File | Rockstar Games Max Payne | Rockstar Games |
| .MP2S | Rockstar Games | Fichiers de jeu | Max Payne 2 Saved Game | Rockstar Games Max Payne | Rockstar Games |
| .MPK | ESRI | Fichiers de jeu | ArcGIS Map Package | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .MPM | Rockstar Games | Fichiers de jeu | Max Payne Modification File | Rockstar Games Max Payne | Rockstar Games |
| .MPN | Synergenix Interactive | Fichiers de jeu | Mophun Game File | Mophun | Synergenix Interactive |
| .MPQ | Blizzard Entertainment Inc. | Fichiers de jeu | Blizzard Mo'PaQ File | MPQ Editor | Open Source |
| .MPR | Open Source | Fichiers de jeu | Bibexcel Data | BibExcel | Open Source |
| .MPS | IBM | Fichiers de jeu | Mathematical Programming System File | Vim | Bram Moolenaar |
| .MPZ | Benetech | Fichiers de jeu | Miradi Project File | Miradi | Benetech |
| .MQO | tetraface Inc. | Fichiers de jeu | Metasequoia Document | Metasequoia | tetraface Inc. |
| .MRK | Microsoft Corporation | Fichiers de jeu | DPOF Auto Print Order File | Microsoft Notepad | Microsoft Corporation |
| .MRS | MAIET Entertainment | Fichiers de jeu | GunZ Game Data File | MAIET Entertainment GunZ | MAIET Entertainment |
| .MS1 | VirtualBus.info | Fichiers de jeu | VirtualBus Map File | VirtualBus | Open Source |
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