| 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 | Adobe Profile Format File |
| apf | Autodesk Showcase Packet 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 |
| apmx86 | Rohitab API Monitor Capture Data |
| app | Alphacam Punch Post Data |
| appcache | HTML5 Application Cache |
| appcontent-ms | Microsoft Windows Application Content |
| 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 |
| apr | Gerber Aperture Data |
| apr | SAM Alignment Probabilities Data |
| apr_lib | Altium Designer Aperture Library Data |
| apt | Alphacam Punch Tool Data |
| apt | Gerber Aperture Data |