| ac$ | Autodesk AutoCAD Temporary File |
| ac0 | HSPICE AC Sweep Waveforms Data |
| ac2 | Banana Accounting Data |
| aca | Microsoft Agent Character Animation |
| aca2 | Fontographer Data |
| acad | Autodesk AutoCAD Database |
| accdu | Microsoft Access Add-in Data |
| acct | IBM AIX Accounting Data |
| acctl | Microsoft InfoPath Data |
| accurip | AccuRIP Data |
| acd | MODTRAN ACD Spectral Output File |
| acdb | Aldec Coverage Database |
| acdb | Android Audio Calibration Database |
| ace | Tablet Assembly Data |
| acelive | Ace Stream Acelive Broadcast Data |
| acf | Microsoft Agent Character Data |
| acff | Volocity Library Clipping Data |
| acg | Microsoft Agent Character Preview |
| acgd | ACG System Predictive Model Data |
| acgl | ACG System License Data |
| ach | Medlin Payroll Software ACH Data |
| ach | NACHA ACH File |
| aci | WebCGM ACI File |
| acis | 3D ACIS Modeler Data |
| ack | Adobe Flash Swifty Extension Data |
| acl | Microsoft Office AutoCorrect List |
| aclcddb | Apple Address Book Changelog Database |
| aclock | Amazing Clock Data |
| acm | Adobe Photoshop Command Button |
| acm | Visual SourceSafe Module Data |
| acmd | API Commander Batch |
| acmi | Tacview Flight Track Data |
| acml | Aircraft Movement Logger Data |
| aco | ArCon Object Collection |
| aco | CYANA Dihedral Angle Constraint File |
