| aam | Adobe Authorware Map |
| aama | Optitex 3D Suite Grading File |
| aan | Avid Pro Tools Analysis Data |
| aao | Agenda At Once Database |
| aapp | Adobe Acrobat AcroApp Script |
| aard | AARD Dictionary Data |
| aas | Adobe Authorware Segment File |
| 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 |
| ab6 | ABstat Data |
| ab8 | ABstat Data |
| aba | AkAbak Abacus Formula Script |
| abb | AlphaBB Data |
| 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 |