| msb | Oracle Binary Message File |
| msct | MOPEKS Script File |
| msh | MaxL Shell Script |
| msh | Microsoft Shell Script |
| msh1 | Microsoft Shell Script |
| msh2 | Microsoft Shell Script |
| msha | Microsoft Help Asset.File |
| mshc | Microsoft Help Container. |
| mshi | Microsoft Help Index.File |
| mshxml | Microsoft Shell Types File |
| msl | ProWorx NXT MSL Loadable |
| mspx | Microsoft Presentation Framework Page |
| mthd | MOPEKS Method File |
| 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 |
| 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 |