| mso | Microsoft Office Rendering Data |
| msor | FiberTrace Data |
| mspdi | Microsoft Project XML Data Interchange File |
| mspm | Nanoeducator File |
| msq | LightShow Pro Media Sequence |
| msr | Mail.dat Manifest Summary File |
| mss | Microprocessor Software Specification |
| msstyles | Windows XP Style Data |
| mst | Gurobi Optimizer MIP Start Data |
| mst | Microsoft Windows Installer Transform |
| msw | Modbus Slave Workspace |
| msy | MicroSyn Data |
| msz | MediaMonkey v3 Compressed Skin |
| mt5 | Poser Material Data |
| mt940 | SWIFT MT940 Customer Statement Message |
| mta | Samsung AllShare Metadata |
| mtb | Minitab Exec File |
| mtc | BrainVoyager QX Mesh Time Course Data |
| mtdd | MEDITECH Document Definition Data |
| mtf | SDL Trados Translation Memory Translations |
| mtg | Making the Grade Data |
| mth | Derive Math File |
| mto | FastCAM MTO Data |
| mtp | SpectraMagic NX Template |
| mtt | MetadataTouch Template |
| mtt | FastCAM MTO Data Template |
| mtw | Minitab Worksheet |
| mub | ExtractNow Data |
| muc | Music Collector Collection Data |
| mud | Textease Database CT Multi-user Database |
