| m3 | Modula-3 Source Code |
| m4 | M4 Macro File |
| m4m | SynDEx Makefile Macro |
| m4x | SynDEx Executive Macro |
| m51 | µVision Listing Data |
| m66 | µVision Listing Data |
| m6m | Mazatrol M640M NC Unit |
| mac | IAR System C-SPY Macro Definition Data |
| mac | UltraEdit Macro |
| magik | Magik Source Code |
| mak | Visual Studio Makefile |
| make | Xcode Make File |
| mako | Mako Template |
| mal | Yaskawa MPE720 v5 Application |
| manifest | Java Manifest File |
| map | IAR System XLink Output Data |
| map | µVision Listing Data |
| markdn | Markdown Document |
| markdown | Markdown Document |
| master | ASP.NET Master Page |
| mat | MATLAB Matrix |
| matlab | MATLAB Script |
| maz | Mazatrol Program |
| mb | MapBasic Source Code |
| mbac | MascotCapsule Resource Data |
| mbas | microBasic Source Code |
| mbo | MapBasic Compiled Object |
| mbrext | Mobirise Extension |
| mbx | MapBasic Program |
| 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 |