| apw | AnyPassword Data File |
| aq | Ancestral Quest Database |
| aq1 | AptiQuiz Test |
| aqa | AptiQuiz Test Result |
| aqa | Ancestral Quest Database Index |
| aqc | AquaChem Database |
| aqg | BenMAP Air Quality Grid |
| aqm | PC 1000 Acquisition Method Data |
| aqm | AlpineQuest Map |
| aqp | Articulate Quizmaker 08 Quiz Data |
| aqr | PC 1000 Acquisition Result Data |
| aqtlb | TestComplete Toolbar Settings Data |
| ar-vmp | BrainVoyager QX Anatomical-resolution Volume Map |
| ar0 | MyDOS Ramdisk Image |
| ar1 | MyDOS Ramdisk Image |
| ar2 | MyDOS Ramdisk Image |
| ar3 | MyDOS Ramdisk Image |
| ar4 | MyDOS Ramdisk Image |
| ar5 | MyDOS Ramdisk Image |
| ar6 | MyDOS Ramdisk Image |
| ar7 | MyDOS Ramdisk Image |
| ar8 | MyDOS Ramdisk Image |
| ar9 | MyDOS Ramdisk Image |
| ara | Archivaldo Resource Archive |
| arb | Alphacam Router VB Macro |
| arc | Tinker Archive |
| arc | AMPAC Archive File |
| arca | RealityCharting Chart File |
| arcade | GameSpy Arcade Data |
| architect | BSS Soundweb London Design Data |
| arcut | Adobe Prelude Rough Cut Data |
| arcutx | Adobe Prelude Rough Cut Data |
| arescol | Ares Galaxy Collection List |
| arf | WebEx Advanced Recording |
| arff | Weka Attribute-Relation File Format |