| m4 | M4 Macro File |
| m4m | SynDEx Makefile Macro |
| m4x | SynDEx Executive Macro |
| m6m | Mazatrol M640M NC Unit |
| mac | UltraEdit Macro |
| magik | Magik Source Code |
| mak | Visual Studio Makefile |
| make | Xcode Make File |
| mako | Mako Template |
| manifest | Java Manifest File |
| markdn | Markdown Document |
| markdown | Markdown Document |
| master | ASP.NET Master Page |
| mat | MATLAB Matrix |
| matlab | MATLAB Script |
| maz | Mazatrol Program |
| mbac | MascotCapsule Resource Data |
| mbas | microBasic Source Code |
| mc | Windows Message Compiler Input |
| mc | Sendmail M4 Configuration Source |
| mcf | Microsoft Shell Console Script |
| mcl | microC Binary File |
| mcr | FactoryTalk View Studio Macro Component File |
| mcw | MPLAB IDE Workspace |
| mdb | ProWorx NXT Memory Data with Blocking |
| mdf | FactoryTalk View Studio Data Log Model |
| mdf | ProWorx NXT Memory Data File |
| mdl | Valve Source Model 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 |
