| mmd | Media Processing Server Audio Data |
| mmd | mAirList Metadata |
| mmdb | Molecular Modeling Database |
| mmdb | MaxMind GeoIP2 Database |
| mme | MIME Encoded Data |
| mmi | Media Processing Server Index File |
| mmjb | MusicMatch Jukebox Data |
| mml | Media Catalog MML File |
| mmmp | MindManager Map Part |
| mmms | MindManager Map Marker List |
| mmo | Memory-Map Overlay File |
| mmr | Inertial Explorer Mounting Data |
| mmr | Sybase PowerDesigner Multimodel Report |
| mmt | Nimbus 7 SAMS MMRVT Data |
| mmu | myPM Merge Data |
| mmw | Microsoft Office Clip Organizer Catalog |
| mmysyscache | Milennial Media Ad Cache |
| mn6 | Microsoft Money 98 Data |
| mn8 | Microsoft Money 8 Data |
| mnc | Autodesk AutoCAD Compiled Menu |
| mnd | Fractal Forge v2 Fractal Parameters |
| mnf | MSC Adams Model Neutral Data |
| mni | Cerious Mandelbrot Image |
| mnk | My Notes Keeper Notebook |
| mnm | Autodesk Character Studio Marker Name |
| mnr | Autodesk AutoCAD Menu Resource |
| mns | Autodesk AutoCAD Menu Source |
| mnu | General CADD Menu |
| mnu | Autodesk AutoCAD Menu Definition |
| mo1 | Magnavox Odyssey 1 Emulator ROM Image |
| moa | MOA Data File |
| mob | MobTV P2P File |
| mod | ArchiCAD Module File |
| mode | Coda Syntax Mode |
| model | Ribbons Model Definition |