| acff | Volocity Library Clipping Data |
| acg | Audio Comparer Group 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 |
| acp | Adobe Acrobat Paper Capture Data |
| acp | EditPlus Auto Completion Data |
| acq | AcqKnowledge Data |
| acq | AcqURL Bookmark Database |
| acr | ACRobot Script |
| acr | Audio Comparer Results Data |
| acrodata | Adobe Acrobat Data File |
| acrotheme | Adobe Acrobat Theme Data |
| acrs | Adobe Authorware Internal Data |
| acrypt | AutoCrypt Blowfish Encrypted Document |
| acrypx | AutoCrypt AES Encrypted Document |
| acrypz | AutoCrypt AES Encrypted Document |
| acs | Microsoft Agent Character |
| acs2 | AIMP 2 Skin File |
| acs3 | AIMP 3 Skin File |
