| attheme | Android Telegram Theme Data |
| attr | Apple iPhoto Image Attributes |
| attx | Cadence OrCAD Attributes Data |
| atv | Act! Data File |
| aty | Topicscape Association Type Data |
| atz | Aston Compiled Theme |
| auc | Microsoft Dynamics AX Application Unicode Object Cache |
| audionote | AudioNote Data |
| audx | ApexSQL Audit Architecture File |
| aue | Annotated Urban Environments Data |
| aui | ArcSoft MediaImpression UI Data |
| aul | AviUtl Language File |
| aum | Adobe Update Manager Data File |
| aur | AutoREALM Map |
| aus | AutoREALM Symbols |
| autoreg | Mozilla Suite Auto Registration Data |
| aux | MOPAC Auxiliary Results Data |
| aux | PTC Creo Auxiliary Parameter Data |
| aux | VecTor5 Auxiliary Data |
| auz | Ableton Live Authorization |
| ava | Animation Master Model |
| ava | BrainVoyager QX ANCOVA Analysis Data |
| ava3 | AVA CAD/CAM Data |
| avastlic | Avast Antivirus License Data |
| avc | Kaspersky Anti-virus Database |
| avd | Avery LabelPro Database |
| avdl | Apache Avro IDL Data |
| avg | AVG Antivirus Virus Database |
| avgdx | AVG Internet Security Diagnostics Data |
| avgf | AVG Internet Security Data |
| avj | Avira AntiVirus Job Data |
| avn | altaVENTE Notes |
| avpr | Apache Avro Protocol Data |
| avro | Avro Serialized Data |
| avsc | Apache Avro Schema |