| mc | Sendmail M4 Configuration Source |
| mc | Windows Message Compiler Input |
| mcf | Microsoft Shell Console Script |
| mcl | microC Binary File |
| mcr | FactoryTalk View Studio Macro Component File |
| mcurl | Curl Manifest Data |
| mcw | MPLAB IDE Workspace |
| mdb | ProWorx NXT Memory Data with Blocking |
| mdes | Trimaran Machine Description Language Data |
| mdf | FactoryTalk View Studio Data Log Model |
| mdf | ProWorx NXT Memory Data File |
| mdl | Valve Source Model Data |
| mdle | Motion Description Language Extended Data |
| mdmp | Windows Debug Dump |
| mdown | Markdown Document |
| mdp | Microsoft Developer Studio Project |
| mdx | Multidimensional Expressions Script |
| mea | FactoryTalk View Studio Project Backup |
| mec | Hitachi Ladder Editor Memo Comment |
| med | FactoryTalk View Studio Development Application |
| mediawiki | MediaWiki Source Code |
| mel | Autodesk Maya Embedded Language Script |
| mep | madExcept Plugin |
| mer | FactoryTalk View Studio Runtime Application |
| mex | MATLAB Executable |
| mexn | MATLAB NeXT Dynamically Linked Subroutines Data |
| mexrs6 | MATLAB IBM RS/6000 Dynamically Linked Subroutines Data |
| mexsg | MATLAB Executable |
| mexw32 | MATLAB Executable |
| mexw64 | MATLAB Executable |
| mf | Java Manifest File |
| mfa | Multimedia Fusion Development Source Data |
| mfa | Multimedia Fusion Source |
| mfcribbon-ms | MFC Ribbon Resource |
| mfd | ABC Monadic Functions Data |