| any | AnyRail Layout Plan |
| aoc | IBM Tivoli Network Manager AOC File |
| aod | Microsoft Dynamics AX Application Object Data |
| aof | Artlantis Object File |
| aom | openEHR Archetype Object Model |
| aop | O&P Industry AOP Data |
| aot | Novell Application Object Template |
| aov | ASReml ANOVA Calculations Data |
| ap11 | Siemens TIA V11 File |
| ap2 | ActivPrimary Resource |
| ap5 | Koyo Screen Creator 5 Transmission File |
| apa | RSView Application Manager Archive |
| apalbum | Apple Aperture Album |
| apb | Alphacam Punch VB Macro |
| apb | LonWorks Binary Neuron Application Image File |
| apdb | Apple Photos Database |
| apdisk | Mac OS X Disk Information File |
| apf | Autodesk Showcase Packet File |
| apf | Adobe Profile Format File |
| apfolder | Apple Photos Folder Data |
| apg | PowerADA APG File |
| api | Adobe Photoshop Ink Colors Setup |
| apin | Adobe InDesign Filter |
| apkg | Anki Exported Flashcard Deck |
| aplibrary | Apple Aperture Library |
| apm | Alphacam Punch Param Macro |
| apmaster | Apple Photos Master Data |
| app | Alphacam Punch Post Data |
| appcache | HTML5 Application Cache |
| appdata | VMware Workstation appData Data |
| appicon | VMware Workstation appData Icon |
| appinfo | VMware Workstation appData Cache |
| appl | BoxGrinder Appliance Data |
| apple | Apple AppleSingle Data |
| application | ClickOnce Deployment Manifest |