| .MSR | Hexagon Mining | Datatiedostot | MineSight Resource Format File | MineSight 3D | Hexagon Mining |
| .MST | Corel | Datatiedostot | Corel Presentations Master Template File | Corel Presentations X8 | Corel |
| .MSVC | Microsoft Corporation | Datatiedostot | Microsoft Visual C++ Compiler Makefile | Microsoft Visual C++ | Microsoft Corporation |
| .MTB | Digistore Solutions | Datatiedostot | MediaTracker Database Backup File | MediaTracker | Digistore Solutions |
| .MTC | Make The Cut, LLC | Datatiedostot | Make The Cut! Project | Make the Cut! | Make The Cut, LLC |
| .MTF | Motorola | Datatiedostot | Motorola Theme File | Motorola MOTOCAST USB | Motorola |
| .MTH | Texas Instruments, Inc. | Datatiedostot | Derive Math File | Texas Instruments Derive | Texas Instruments, Inc. |
| .MTM | VideoLAN | Datatiedostot | MultiTracker Module | VLC Media Player | VideoLAN |
| .MTS | Sony | Datatiedostot | AVCHD Video File | Microsoft Windows Media Player | Microsoft Corporation |
| .MTT | Digital Confidence | Datatiedostot | MetadataTouch Template | Digital Confidence MetadataTouch | Digital Confidence |
| .MTW | Minitab Inc | Datatiedostot | Minitab Worksheet File | Minitab | Minitab Inc |
| .MUF | Alpha Software | Datatiedostot | Alpha Five License File | Alpha Anywhere - Alpha Software | Alpha Software |
| .MUM | AmsterCHEM | Datatiedostot | MATLAB Unit Operation Model File | AmsterCHEM MATLAB CAPE-OPEN Unit Operation | AmsterCHEM |
| .MUP | Lauriso Software | Datatiedostot | Music Publisher Score | Music Publisher | Lauriso Software |
| .MVE | BioWare | Datatiedostot | Infinity Engine Movie File | Baldur's Gate | BioWare |
| .MVP | Magix Software GmbH | Datatiedostot | MAGIX Video Project File | MAGIX Video Pro X | Magix Software GmbH |
| .MW | Apple | Datatiedostot | MacWrite Text Document | MacWrite | Apple |
| .MWF | Autodesk, Inc. | Datatiedostot | MapGuide Author Map Window File | Infrastructure Map Server | Autodesk, Inc. |
| .MWS | Waterloo Maple, Inc. (Maplesoft) | Datatiedostot | Maple Classic Worksheet | Maple | Waterloo Maple, Inc. (Maplesoft) |
| .MWV | Unknown Developer | Datatiedostot | Media Works Data | Unknown Software | Unknown Developer |
| .MX | Wolfram Research | Datatiedostot | Mathematica Serialized Package File | Wolfram Research Mathematica | Wolfram Research |
| .MXC2 | Magix Software GmbH | Datatiedostot | MAGIX Cache File | MAGIX Music Maker | Magix Software GmbH |
| .MXI | Adobe Systems Incorporated | Datatiedostot | Adobe Extension Information File | Adobe InCopy | Adobe Systems Incorporated |
| .MXM | Next Limit Technologies | Datatiedostot | Maxwell Material File | Maxwell Render | Next Limit Technologies |
| .MXP | Adobe Systems Incorporated | Datatiedostot | Adobe Extension Package | Adobe Extension Manager CC | Adobe Systems Incorporated |
| .MYB | MYOB Limited | Datatiedostot | MYOB Data File | MyOB | MYOB Limited |
| .MYI | Oracle Corporation | Datatiedostot | MySQL MyISAM Index File | MySQL | Oracle Corporation |
| .MYO | Acclivity LLC | Datatiedostot | AccountEdge Company File | AccountEdge Pro | Acclivity LLC |
| .MZE | Gregory Peatfield | Datatiedostot | Maze Creator File | Maze Creator | Gregory Peatfield |
| .MZT | David Webber | Datatiedostot | MOZART Template File | Mozart | David Webber |
| .MZV | Viewpoint Corporation | Datatiedostot | Viewpoint Media Player ZoomView File | Viewpoint Media Player | Viewpoint Corporation |
| .MZX | MegaZeux Developers | Datatiedostot | MegaZeux Data | MegaZeux | MegaZeux Developers |
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