| mdm | BrainVoyager QX MDM Data |
| mdn | Microsoft Access Blank Database Template |
| mdo | Microsoft IIS Metabase Backup |
| mdp | GROMACS Molecular Dynamics Program |
| mdpd | Trajexia Saved Parameters Data |
| mdq | Database Interface Designer Database Query DaTa |
| mdr | ZX Spectrum Emulator Microdrive Cartridge Data |
| mdsx | MEGA Saved Session |
| mdu | D-Flow FM Model Definition Unstructured Data |
| mdus | MessengerDiscovery Internal Data |
| mdv | SmartWare Modem Definition Data |
| mdw | Microsoft Access Workgroup Data |
| mdx | dBASE IV Multiple Index |
| mdy | Sprint RSS iDEN Contact List Data |
| meb | PRO100 3D Interior Catalog Element |
| mechdat | ANSYS Mechanical Exported Data |
| mechdb | ANSYS Mechanical Database |
| meg | MEGA Data |
| mega | Megacubo XML Metafile |
| mem | E-Sword v8 Memory Verses Data |
| mem | Medical Expense Manager Data |
| mem | Virtual Game Station Memory Card |
| memb | PTC Creo Assembly Member Information Data |
| meme | MEME Motif Format Data |
| memo | S Memo Data |
| memx | E-Sword v9 Memory Verses Data |
| menc | Windows Mobile Encrypted File |
| menu | Zoom Player Menu Text Data |
| menuskin | ObjectBar Menu Skin |
| mep | Inor MePro Data |
| meps | MEPS Data |
| meq | Corel WordPerfect Macro Editor Print Queue |
| mes | SpectraMagic NX Data |
| mes | TrimeTool MES Output |
| mesa | MESA Model |