| mif | Adobe FrameMaker Interchange Format |
| mind | MindMeister Mindmap Document |
| mjb | MuJoCo Binary Model |
| mjbooktemplate | MacJournal Book Template |
| mjcf | MuJoCo XML Model |
| mjdoc | MacJournal Document |
| mkd | CAD6 Drawing |
| mkd | MarkDown Document |
| mlb | Lotus Symphony Macro Library |
| mli | Autodesk 3D Studio Material Library |
| 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 |
| 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 |