| mnl | Help and Manual Print Manual Template |
| mnp | Ultrasoft Money Document |
| mny | Microsoft Money Data |
| moi | Readme Text |
| montage | Montage Screenplay Document |
| mosaic | MacOSaiX Mosaic |
| mpf | Microsoft Media Package File |
| mpp | Microsoft Project Document |
| mppx | Microsoft Project Document |
| mps | Garmin MapSource Document |
| mpt | Microsoft Project Template |
| mpx | Microsoft Project Exchange Document |
| mrc | MARC Document |
| mrd | MathRevolt Ininity Document |
| mrml | 3D Slicer Scene Description |
| mrml | Medical Reality Modeling Language File |
| mro | SharpEye Music Reader Document |
| mrp | MathRevolt Ininity Plot |
| ms10 | NI Multisim 10 Circuit Design |
| ms11 | NI Multisim 11 Circuit Design |
| ms12 | NI Multisim 12 Circuit Design |
| ms13 | NI Multisim 13 Circuit Design |
| ms14 | NI Multisim 14 Circuit Design |
| ms3d | MilkShape 3D Model |
| ms7 | NI Multisim 7 Circuit Design |
| ms8 | NI Multisim 8 Circuit Design |
| ms9 | NI Multisim 9 Circuit Design |
| mscx | MuseScore Music Score |
| mscz | MuseScore Compressed Music Score |
| msg | Microsoft Outlook E-Mail Message |
| msim | MapleSim Model |
| mtd | Musicnotes Digital Sheet Music |
| mtf | MasterCook Document |
| mts | Viewpoint MTS Document |
| mud | Autodesk Mudbox Model |