| 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 |
| 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 |
| 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 |
| ndx | WinDev HyperFileSQL Index |
| ned | OMNeT++ Network Description |
| neko | Neko Source Code |
| nesl | NESL Source Code |
| nfm | Delphi .NET Form |
| nfx | NetObjects Fusion Components |
| ngi | NGI Package |
| ngo | Norton Guide Linker Object |
| nhs | NHibernate Settings File |
