| abbu | Mac OS X Address Book Backup |
| abc | Act! Database Index |
| abc | Alembic Data |
| abcddb | Apple Address Book Contact List Database |
| abcdmr | Apple Address Book Mail Recent Data |
| abcdp | Address Book CoreData Person Data |
| abd | The Bat! Address Book |
| abdata | Adobe Bridge Keywords Database |
| abe | NoScript Application Boundaries Enforcer Data |
| abf2 | Axon pCLAMP ABF2 Data |
| abicollab | AbiCollab Collaborative File Descriptor Data |
| abk | CorelDraw AutoBackup |
| abk | Kodak EasyShare Addressbook Data |
| abl | ADONIS Application Business Library |
| abnf | Augmented Backus-Naur Form |
| aboc | Edge Boundary Condition Data |
| abp | AVS Barcode Source Profile |
| abq | Abaqus/Explicit State Data |
| abs | Rocket D3 Executable Object Module Data |
| abu | Act! Database Index |
| abx | Corel WordPerfect Mail Addressbook |
| aby | AOL Desktop Address Book |
| abz | Pro/ENGINEER AutobuildZ Data |
| ac | CaseWare Working Papers Client File |
| ac$ | Autodesk AutoCAD Temporary File |
| ac0 | HSPICE AC Sweep Waveforms Data |
| ac2 | Banana Accounting Data |
| aca | Microsoft Agent Character Animation |
| accdu | Microsoft Access Add-in Data |
| accurip | AccuRIP Data |
| acd | MODTRAN ACD Spectral Output File |
| acdb | Aldec Coverage Database |
| acdb | Android Audio Calibration Database |
| ace | Tablet Assembly Data |
| acf | Microsoft Agent Character Data |