| mtn | Monotone Database |
| mtpf | Moony-TexturePacker Texture |
| mtra | MascotCapsule Resource Data |
| mtrl | Esenthel Engine Material Data |
| mtxt | MOPEKS Text File |
| mu | MuPAD Source Code |
| muf | Alpha Five Concurrent Users Data |
| mui | Multilingual User Interface Data |
| mv | Miva Script Source Code |
| mvc | Compiled Miva Script Program |
| mvq | mvQuery Query |
| mvt | Miva Merchant Module |
| mvx | Multimedia Fusion Movement Extension |
| mx | Modula-3 Linker Information |
| mxe | Max Windows 32-bit External Object |
| mxe64 | Max Windows 64-bit External Object |
| mxl | MaxL Script |
| mxls | MaxL Encyrpted Script |
| mxml | Adobe Flex Markup Language |
| mxo | Max Macintosh External Object |
| myapp | Visual Studio Application XML |
| mz | Mezzo Source Code |
| mzb | MegaZeux Board Data |
| mzi | Mezzo Interface File |
| mzx | MegaZeux World |
| n | Neko Bytecode |
| nb0 | Windows CE Boot Loader Image |
| nbc | Next Byte Codes Source Code |
| nbin | Compiled NASL Script |
| ncb | Visual Studio No Compile Browse File |
| ncl | NCAR Command Language File |
| ndb | ProWorx NXT Short Comment with Blocking |
| ndf | ProWorx NXT Short Comment File |
| ndll | Neko Dynamic Library |
| ndx | WinDev HyperFileSQL Index |
