| aat | ArchiCAD Attributes Data |
| aatrend | ActiveFactory Trend Data |
| aaui | Adobe Acrobat User Interface Data |
| aawdef | Ad-Aware Definitions Data |
| ab1 | DNA Electropherogram File |
| ab3 | PhotoImpact 3 Album |
| ab4 | Eniac AB4 Data |
| ab6 | ABstat Data |
| ab8 | ABstat Data |
| aba | AkAbak Abacus Formula Script |
| abb | AlphaBB Data |
| abbu | Mac OS X Address Book Backup |
| abc | ABC-View Manager Thumbnail Cache |
| abc | Act! Database Index |
| abc | Alembic Data |
| abcd | AudioVisual Book Data |
| abcddb | Apple Address Book Contact List Database |
| abcdmr | Apple Address Book Mail Recent Data |
| abcdp | Address Book CoreData Person Data |
| abd | Intuit Quicken Address Book Add-on 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 | HP 95LX Appointment Book Data |
| abk | Kodak EasyShare Addressbook Data |
| abl | ADONIS Application Business Library |
| abl | Maxagrid Avails Data |
