| arff | Weka Attribute-Relation File Format |
| arg | Autodesk AutoCAD User Profile |
| arlnk | Ares Galaxy Link Data |
| arm | Alphacam Router Param Macro |
| arm | Armadillo Protected File |
| armodel | Kudan AR Model |
| arp | Alphacam Router Post Data |
| arpack | ArtRage Package File |
| ars | Adobe After Effects Render Settings |
| arscript | ArtRage Script File |
| art | Alphacam Router Tool Data |
| arti | Artizen HDR Data |
| artpro2 | Arturia Prophet V Data |
| artwork | iOS Artwork Data |
| arv | CA Harvest SCM Data |
| arxml | AUTOSAR XML Data |
| arz | MySQL Archive Storage Engine Data |
| as2 | Activstudio Data |
| as2 | Time Stamp Project Grid Information |
| as3a | ActivInspire Resource Pack |
| as4 | AskSam Database Backup |
| as4a | ActivInspire Resource Pack |
| asas | ANSYS ASAS Input File |
| asat | TurboCAD Assemble SAT 3D Model |
| asb | Alphacam Stone VB Macro |
| asc | Autodesk 3D Studio Scene in ASCII |
| asc | SOBEK RTC Communication Data |
| asce | ASCE Data |
| asd | Ableton Warp Analysis File |
| ashlang | Ashampoo Media Player Language Data |
| asice | DigiDoc BDOC Digital Signature |
| asif | AEDT Standard Input Data |
| asj | Aldfaer Data File |
| ask | Ableton Live Skin |
| ask | AskSam Database |