| .MISC | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MJ3 | id Software | Datatiedostot | Id Software Online Sale File | Doom | id Software |
| .MJG | Bitdefender | Datatiedostot | Trojan Data | AVG Antivirus | AVG Technologies |
| .MJK | Konyisoft | Datatiedostot | Question File | Nosza, legyél má' te is MILIJOMOS! | Konyisoft |
| .MJM | Unknown Developer | Datatiedostot | JDF Data Exchange Format | Unknown Software | Unknown Developer |
| .MJR | JRiver | Datatiedostot | Media Jukebox Registration Data | Media Jukebox | JRiver |
| .MKR | Microsoft Corporation | Datatiedostot | Train Simulator Marker File | Microsoft Train Simulator | Kuju Entertainment |
| .MKS | Matroska | Datatiedostot | Matroska Elementary Stream File | The Core Media Player | Open Source |
| .ML3 | KIDASA Software, Inc. | Datatiedostot | Milestones V3 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML4 | KIDASA Software, Inc. | Datatiedostot | Milestones 4 Schedule File | Milestones Professional | KIDASA Software, Inc. |
| .ML5 | KIDASA Software, Inc. | Datatiedostot | Milestones V5 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML6 | KIDASA Software, Inc. | Datatiedostot | Professional 2000 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .ML7 | KIDASA Software, Inc. | Datatiedostot | Milestones Professional 2002 Project | Milestones Professional | KIDASA Software, Inc. |
| .ML8 | KIDASA Software, Inc. | Datatiedostot | Milestones Professional 2004 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .ML9 | KIDASA Software, Inc. | Datatiedostot | Milestones Professional 2004 Schedule | Milestones Professional | KIDASA Software, Inc. |
| .MLA | Unknown Developer | Datatiedostot | WorshipCenter Pro Document | WorshipCenter Pro | Interscape |
| .MLB | Avanquest Software | Datatiedostot | MyLabel Designer Deluxe Project File | MyLabel Designer Deluxe | Avanquest Software |
| .MLC | Microsoft Corporation | Datatiedostot | Microsoft Language Interface Pack | Microsoft Windows | Microsoft Corporation |
| .MLD | FMJ-Software | Datatiedostot | I-Melody Format For I-Mode | Awave Studio | FMJ-Software |
| .MLI | Unknown Developer | Datatiedostot | Encyclopedia Media List | Unknown Software | Unknown Developer |
| .MLM | Agile Molecule | Datatiedostot | MolMeccano File | Abalone | Agile Molecule |
| .MLN | Autodesk, Inc. | Datatiedostot | AutoCAD Multiline Definition Data File | Autodesk AutoCAD | Autodesk, Inc. |
| .MLP | Meridian Audio | Datatiedostot | Meridian Lossless Packing Audio File | MLP Professional Encoder Software | Meridian Audio |
| .MLS | KIDASA Software, Inc. | Datatiedostot | Milestones Simplicity File | Milestones Professional | KIDASA Software, Inc. |
| .MLT | Business Forecast Systems, Inc. | Datatiedostot | Multivariate Forecast File | Forecast Pro | Business Forecast Systems, Inc. |
| .MLTV | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MM | Kodak | Datatiedostot | Kodak EasyShare Thumbnail Cache File | Kodak EasyShare | Kodak |
| .MMA | Open Source | Datatiedostot | Master Album Maker Photo Album File | Master Album Maker Viewer | Open Source |
| .MMAP | Mindjet | Datatiedostot | MindManager Map File | MindManager | Mindjet |
| .MMB | Mediachance | Datatiedostot | MultiMedia Builder Data | MediaChance Multimedia Builder | Mediachance |
| .MMC | Microsoft Corporation | Datatiedostot | Microsoft Media Catalog | Microsoft Office | Microsoft Corporation |
| .MMD | Cumulate Labs | Datatiedostot | Cumulate Draw Editable File | Cumulate Draw | Cumulate Labs |
| .MMF | Microsoft Corporation | Datatiedostot | Microsoft Message File | Microsoft Exchange Server | Microsoft Corporation |
| .MMM | Magix Software GmbH | Datatiedostot | Music Maker Arrangement File | MAGIX Music Maker | Magix Software GmbH |
| .MMP | MixMeister Technology | Datatiedostot | MixMeister Studio Playlist | MixMeister Studio | MixMeister Technology |
| .MMR | Fuji Xerox | Datatiedostot | Fuji Xerox Fax Image | FaxSee Pro | SFaxTools |
| .MMS | Nokia | Datatiedostot | Multimedia Messaging Service Message | Nokia Suite | Nokia |
| .MMT | Open Source | Datatiedostot | Nimbus 7 SAMS Data File | Microsoft Notepad | Microsoft Corporation |
| .MN | MathWorks | Datatiedostot | MATLAB Data | The MathWorks MATLAB | MathWorks |
| .MN2 | Interplay Entertainment | Datatiedostot | Descent 2 Mission File | Interplay Descent 2 | Interplay Entertainment |
| .MN7 | Microsoft Corporation | Datatiedostot | Microsoft Money (Ver 7) Data File | Microsoft Money | Microsoft Corporation |
| .MN9 | Microsoft Corporation | Datatiedostot | Microsoft Money File | Intuit Quicken | Quicken |
| .MNC | Autodesk, Inc. | Datatiedostot | AutoCAD Compiled Menu File | Autodesk AutoCAD | Autodesk, Inc. |
| .MND | Autodesk, Inc. | Datatiedostot | AutoCAD Menu Compiler File | Autodesk AutoCAD | Autodesk, Inc. |
| .MNO | Adobe Systems Incorporated | Datatiedostot | Macromedia Design Note | Adobe Dreamweaver | Adobe Systems Incorporated |
| .MNY | Microsoft Corporation | Datatiedostot | Microsoft Money File | Intuit Quicken | Quicken |
| .MO | Dassault Systèmes | Datatiedostot | Dymola Simulation File | Dymola | Dassault Systèmes |
| .MOD | Open Source | Datatiedostot | Amiga Music Module File | ModPlug Player | Open Source |
| .MODEM | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MOHO | Smith Micro Software | Datatiedostot | Moho Animation Project | Smith Micro Moho Debut 12 | Smith Micro Software |
| .MOL | Interscape | Datatiedostot | MDL Molfile | Avogadro | Open Source |
| .MOL2 | Tripos | Datatiedostot | Tripos Mol2 Format File | Open Babel | Open Babel development team |
| .MONEY | Jumsoft | Datatiedostot | Money Data File | Jumsoft Money | Jumsoft |
| .MOOD | Open Source | Datatiedostot | Amarok Moodbar Data File | Amarok | Open Source |
| .MOP | James Stewart | Datatiedostot | MOPAC Input Format | MOPAC | James Stewart |
| .MOR | Corel | Datatiedostot | Corel Shared Writing Tools Data | Corel Paradox | Corel |
| .MOS | MamiyaLeaf | Datatiedostot | Leaf Camera RAW File | MacPhun ColorStrokes | Macphun |
| .MOT | NewTek | Datatiedostot | LightWave Motion File | LightWave 3D | NewTek |
| .MOUSE | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MOVEMON | Unknown Developer | Datatiedostot | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .MOX | Imagine That Inc. | Datatiedostot | ExtendSim Simulation Software Model | ExtendSim | Imagine That Inc. |
| .MP0 | Sony | Datatiedostot | Sony Ericsson GPEH Session | Sony Ericsson GPEH | Sony |
| .MP5 | Waterloo Maple, Inc. (Maplesoft) | Datatiedostot | Maple File | Maple | Waterloo Maple, Inc. (Maplesoft) |
| .MP6 | Unknown Developer | Datatiedostot | CS225 MP6 Huffman Encoding Text Data | Unknown Software | Unknown Developer |
| .MPCB | ReliaSoft | Datatiedostot | ReliaSoft MPC Data | ReliaSoft MPC | ReliaSoft |
| .MPD | Microsoft Corporation | Datatiedostot | Microsoft Project Database | Microsoft Office | Microsoft Corporation |
| .MPF | Microsoft Corporation | Datatiedostot | Microsoft Media Package File | Microsoft Clip Organizer | Microsoft Corporation |
| .MPH | Magix Software GmbH | Datatiedostot | Photostory Deluxe Project | MAGIX Photostory 2016 Deluxe | Magix Software GmbH |
| .MPI | Open Source | Datatiedostot | InstallJammer Project File | InstallJammer | Open Source |
| .MPJ | Minitab Inc | Datatiedostot | Minitab Project File | Minitab | Minitab Inc |
| .MPP | Microsoft Corporation | Datatiedostot | Microsoft Project File | Serena OpenProj | Serena |
| .MPQE | Blizzard Entertainment Inc. | Datatiedostot | Blizzard Encrypted Mo'PaQ File | Blizzard StarCraft 2 | Blizzard Entertainment Inc. |
| .MPR | Open Source | Datatiedostot | Bibexcel Data | BibExcel | Open Source |
| .MPS | IBM | Datatiedostot | Mathematical Programming System File | Vim | Bram Moolenaar |
| .MPT | Microsoft Corporation | Datatiedostot | Microsoft Project Template | Microsoft Project 2016 | Microsoft Corporation |
| .MPX | Microsoft Corporation | Datatiedostot | FoxPro Compiled Menu Program | Microsoft Visual FoxPro | Microsoft Corporation |
| .MPZ | Benetech | Datatiedostot | Miradi Project File | Miradi | Benetech |
| .MQD | Open Source | Datatiedostot | Malete Query Data File | Malete | Open Source |
| .MQP | GoldWave Inc. | Datatiedostot | Multiquence Project | Multiquence | GoldWave Inc. |
| .MRC | mIRC Co. Ltd | Datatiedostot | mIRC Script File | mIRC | mIRC Co. Ltd |
| .MRD | Interscape | Datatiedostot | MathRevolt Infinity Document | Infinity | Interscape |
| .MRF | Apple | Datatiedostot | Macintosh Font File | Apple OS X | Apple |
| .MRI | Open Source | Datatiedostot | Pittsburgh MRI File Format | PGH_MRI | Open Source |
| .MRO | Graham Jones | Datatiedostot | SharpEye Music Reader File | SharpEye Music Reader | Graham Jones |
| .MRP | Interscape | Datatiedostot | Infinity Solution Plot Data | Infinity | Interscape |
| .MRX | Open Source | Datatiedostot | Record Access File | Malete | Open Source |
| .MS-ONE-STUB | Microsoft Corporation | Datatiedostot | Microsoft OneNote Stub Data | Microsoft OneNote | Microsoft Corporation |
| .MS-WINDOWS-STORE-LICENSE | Microsoft Corporation | Datatiedostot | Microsoft Windows License Manager Data | Microsoft Windows | Microsoft Corporation |
| .MS8 | National Instruments | Datatiedostot | Multisim 8 Circuit Design File | NI Multisim | National Instruments |
| .MSB | Oracle Corporation | Datatiedostot | Oracle Binary Message File | Oracle Database | Oracle Corporation |
| .MSC | Microsoft Corporation | Datatiedostot | Microsoft C Makefile | Microsoft Visual C++ | Microsoft Corporation |
| .MSD | ESRI | Datatiedostot | Map Service Definition File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .MSF | Mozilla | Datatiedostot | Mail Summary File | Mozilla Thunderbird | Mozilla |
| .MSG | Microsoft Corporation | Datatiedostot | Saved Email Message | Microsoft Outlook Express | Microsoft Corporation |
| .MSG2 | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .MSIF | Avanquest Software | Datatiedostot | MyLabel Designer Deluxe Data File | MyLabel Designer Deluxe | Avanquest Software |
| .MSK | Corel | Datatiedostot | Paint Shop Pro Mask File | PaintShop Pro | Corel |
| .MSN | Microsoft Corporation | Datatiedostot | Host Blocking File | Microsoft Windows | Microsoft Corporation |
| .MSO | Microsoft Corporation | Datatiedostot | Microsoft Organization Chart Data File | Microsoft Organization Chart | Microsoft Corporation |
| .MSP | Microsoft Corporation | Datatiedostot | Windows Installer Patch | Windows Installer | Microsoft Corporation |
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