| mdl | STAR-CD v4 Model Data |
| mdl | Cognos Exported Model Data |
| mdl | Bentley MicroStation MDL Program |
| mdl | Animation Master Model Data |
| mdl0 | Nintendo Wii Model Data |
| mdm | OvenWATCH Dataset |
| mdm | HLM Multivariate Data Matrix |
| 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 |
| mds | PLINK Multidimensional Scaling Report Data |
| mdsx | MEGA Saved Session |
| mdtext | Markdown Text Data |
| mdtxt | Markdown Text Data |
| mdu | D-Flow FM Model Definition Unstructured Data |
| mdus | MessengerDiscovery Internal Data |
| mdv | SmartWare Modem Definition Data |
| mdw | Microsoft Access Workgroup Data |
| mdx | MDict Dictionary Data |
| mdx | dBASE IV Multiple Index |
| mdy | Sprint RSS iDEN Contact List Data |
| mea | Mastersizer 2000 Data |
| meb | PRO100 3D Interior Catalog Element |
| mechdat | ANSYS Mechanical Exported Data |
| mechdb | ANSYS Mechanical Database |
| mecontact | Live Messenger Contacts Data |