| mli | Autodesk 3D Studio Material Library |
| mlj | Canon MultiPASS Suite Fax Document |
| mlk | MasterCook Look Data |
| mlm | Novell GroupWise Saved E-Mail |
| mlp | Label Designer Plus Document |
| mlr | Mollier Sketcher Document |
| mma | Master Album Maker Document |
| mml | Mathematical Markup Language Document |
| mmp | MindManager 2002 Map Document |
| mmpt | MindManager 2002 Map Template |
| mmsw | Movie Magic Screenwriter Document |
| mn | MuPAD Notebook Document |
| mnb | MuPAD Notebook Document |
| mnl | Help and Manual Print Manual Template |
| mnp | Ultrasoft Money Document |
| mny | Microsoft Money Data |
| montage | Montage Screenplay Document |
| mosaic | MacOSaiX Mosaic |
| mpd | LDraw Multi-Part Document |
| 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 |
| mrcx | MARC21 XML Schema |
| 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 |