| ahtml | Amulet Module Main OS File |
| aidl | Android Interface Definition Language Data |
| aio | APL Transfer Format File |
| aj | AspectJ Source Code |
| al11 | SAP ABAP AL11 Transaction Code |
| alan | Alan v3 Source Code |
| alb | Alpha Five Library |
| alm | Alpha Five Data |
| alx | Alpha Five Script Data |
| am | GNU Automake Input File |
| amos | AMOS Source Code |
| ane | Adobe AIR Native Extension |
| ani | Valve Source Model Animation Data |
| ansym | Adobe Edge Animate Symbol Data |
| anv | Anastasia Style |
| aop | JBoss AOP File |
| ap | WebSuite Active Page |
| ap3 | VS10XX VSOS Application |
| api | WebObjects API File |
| aplt | AppleScript Applet |
| app | Visual FoxPro Application |
| applescript | AppleScript Script Bundle |
| applescript | AppleScript Script |
| appup | Erlang Application Upgrade File |
| appx | Microsoft Windows 8 App Package |
| appxbundle | Microsoft Windows 8.1 App Bundle Package |
| appxbundlemanifest | Microsoft Windows 8.1 App Bundle Manifest File |
| appxsym | Windows 8 App Package Symbols |
| appxupload | Windows 8 App Upload Package |
| aps | VS Binary Resource Script Data |
| apx | WebSuite Compiled Active Page |
| aqf | Aquifer CMS Page |
| arc | BASIS ASCII Resource Data |
| armi | Carbide ARMI Project |
| arnoldc | ArnoldC Source Code |