| 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 | Android Audio Calibration Database |
| acdb | Aldec Coverage Database |
| ace | Tablet Assembly Data |
| acf | Microsoft Agent Character Data |
| acff | Volocity Library Clipping Data |
| acg | Microsoft Agent Character Preview |
| ach | NACHA ACH File |
| aci | WebCGM ACI File |
| acis | 3D ACIS Modeler Data |
| ack | Swifty Extension Data |
| acl | Microsoft Office AutoCorrect List |
| acm | Adobe Photoshop Command Button |
| acml | Aircraft Movement Logger Data |
| aco | CYANA Dihedral Angle Constraint File |
| aco | ArCon Object Collection |
| acq | AcqKnowledge Data |
| acr | ACRobot Script |
| acrodata | Adobe Acrobat Data File |
