| mskn | MediaMonkey Skin |
| 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 |
| mss | WRAP Message Data |
| mssp | mIRC Script Setup Creator Data |
| msstyle | Windows XP Unsigned Style |
| msstyles | Windows XP Style Data |
| mst | Microsoft Windows Installer Transform |
| mst | Gurobi Optimizer MIP Start Data |
| mstat | SAM Domain Output Data |
| mstr | MicroStrategy Dashboard Data |
| msty | Muvee Automatic Video Editing Style |
| 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 |
| mtbl | PIPE-FLO Motor Data Table |
| mtc | BrainVoyager QX Mesh Time Course Data |
| mtf | SDL Trados Translation Memory Translations |
| mtg | Making the Grade Data |
| mth | Derive Math File |
| mtkey | proDAD Heroglyph License Data |
| mtn | PTC Creo Tool Motion Parameter Data |
| mto | FastCAM MTO Data |
| mtp | SpectraMagic NX Template |
| mtst | MotionTracking RAW Image Stack Data |
| mtt | FastCAM MTO Data Template |