File extensions start with character 'A'
| File Type | Category | File Format | |
|---|---|---|---|
| .a | Development Files | Static Library | |
| .a00 | Archive Files | ALZip Second Split Archive File | |
| .a2m | Audio Files | AdLib Tracker 2 File | |
| .a2theme | Configuration Files | Aston 2 Theme File | |
| .a3l | Data Files | Authorware 3 Library | |
| .a3m | Data Files | Authorware 3 Macintosh File | |
| .a3w | Data Files | Authorware 3 Windows File | |
| .a4l | Data Files | Authorware 4 Library | |
| .a4m | Data Files | Authorware 4 Macintosh File | |
| .a4w | Data Files | Authorware 4 Windows File | |
| .a52 | Game Files | Atari 5200 ROM | |
| .a5l | Data Files | Authorware 5 Library | |
| .a5w | Web Files | Alpha Five Webpage File | |
| .a65 | Data Files | Authorware 6.5 File | |
| .aa | Audio Files | Audible Audio Book File | |
| .aa3 | Audio Files | ATRAC Audio File | |
| .aac | Audio Files | Advanced Audio Coding File | |
| .aam | Data Files | Authorware Map File | |
| .aax | Audio Files | Audible Enhanced Audiobook File | |
| .ab | Backup Files | Android ADB Backup File | |
| .ab1 | Data Files | DNA Electropherogram File | |
| .ab2 | Data Files | Print Shop Address Book File | |
| .ab3 | Data Files | PhotoImpact 3 Album File | |
| .aba | Backup Files | Palm Address Book Archive | |
| .abbu | Backup Files | Address Book Backup | |
| .abc | Audio Files | ABC Music Notation | |
| .abcd | Data Files | AudioVisual Book Data File | |
| .abdata | Data Files | Adobe Bridge Data File | |
| .abf | Backup Files | Analysis Services Backup File | |
| .abi | Data Files | DNA Chromatogram File | |
| .abk | Backup Files | Automatic Backup File | |
| .abkprj | Data Files | Ashampoo Backup Project | |
| .abm | Raster Graphics Files | Photo Album | |
| .abp | Data Files | AVS Barcode Profile | |
| .abr | Multiple Use Files | Adobe Photoshop Brushes File | |
| .abs | Data Files | Absolute Database File | |
| .abs | Game Files | AB SuDoKu Saved Game | |
| .abw | Text Files | AbiWord Document | |
| .aby | Data Files | AOL Address Book File | |
| .ac3 | Audio Files | Audio Codec 3 File | |
| .aca | Data Files | Agent Character Animation File | |
| .acc | Data Files | Graphics Accounts Data File | |
| .accda | Plug-in Files | Access Add-in File | |
| .accdb | Microsoft Access Files | Access 2007 Database File | |
| .accde | Microsoft Access Files | Access Execute Only Database | |
| .accdt | Database Files | Microsoft Access Database Template | |
| .accountpicture-ms | Raster Graphics Files | Windows 8 Account Picture File | |
| .acd | Audio Files | ACID Project File | |
| .acd-bak | Audio Files | Sony ACID Project Backup File | |
| .acd-zip | Audio Files | Sony ACID Project With Embedded Media File | |
| .ace | Compressed Files | WinAce Compressed File | |
| .acf | Filter Files | Steam Application Cache File | |
| .acf | Data Files | Agent Character Data File | |
| .acg | Data Files | Agent Preview File | |
| .acl | Partially Downloaded Files | AutoCorrect List File | |
| .acm | Audio Files | Interplay Audio File | |
| .aco | Configuration Files | Adobe Photoshop Color Swatch File | |
| .acp | Backup Files | Alfresco Content Package | |
| .acs | Partially Downloaded Files | Agent Character File | |
| .act | Adobe Files | ADPCM Compressed Audio File | |
| .act | 3D Graphics Files | Genesis3D Actor File | |
| .ad3 | Audio Files | Adaptive PCM Sound Voice File | |
| .ada | Development Files | Ada Source Code | |
| .adb | Database Files | Alpha Five Database File | |
| .adb | Development Files | Ada Body File | |
| .adf | Data Files | ESRI ArcInfo Binary Grid Format | |
| .adg | Audio Files | Ableton Device Group | |
| .adi | Backup Files | Active@ Disk Image Backup File | |
| .adm | System Files | Administrative Template File | |
| .adn | Database Files | Access Blank Project Template | |
| .ads | Development Files | Ada Specification File | |
| .adt | Data Files | ACT! Document Template | |
| .adts | Audio Files | Audio Data Transport Stream File | |
| .adu | Data Files | Addict User Dictionary File | |
| .adv | Device Driver Files | Nortek Acoustic Doppler Velocimeter File | |
| .adx | Database Files | Approach Index File | |
| .aec | Digital Video Files | Cinema 4D After Effects Composition | |
| .aep | Digital Video Files | After Effects Project | |
| .afc | Audio Files | Mass Effect 2 Audio File | |
| .afe | Data Files | Avid File Exchange File | |
| .afl | Font Files | Adobe Font Metrics File | |
| .afp | Document Files | Advanced Function Presentation File | |
| .aft | Data Files | Ancestry.com Family Tree Database | |
| .agd | Data Files | AgileGraph Data File | |
| .aggr | Data Files | Adobe Captivate Aggregate File | |
| .agm | Audio Files | DTS Multi-channel Pro Packer File | |
| .ahk | Program Execution Files | AutoHotkey Script | |
| .ai | Vector Graphics Files | Adobe Illustrator File | |
| .aif | Audio Files | Audio Interchange File Format | |
| .aifb | Data Files | AIF Builder Project File | |
| .aifc | Audio Files | Compressed Audio Interchange File | |
| .aiff | Audio Files | Audio Interchange File Format | |
| .aim | Text Files | AIMMS ASCII Model File | |
| .air | Program Execution Files | Adobe AIR Installation Package | |
| .ais | Raster Graphics Files | ACDSee Image Sequence File | |
| .ais | Data Files | HP NewWave Cardfile Application Data File | |
| .aiv | Data Files | AIVault Data File | |
| .akp | Audio Files | Akai Sampler File | |
| .al | Audio Files | A-Law Compressed Sound Format | |
| .alac | Audio Files | ALAC Encoded Audio File | |
| .alaw | Audio Files | A-Law Compressed Sound Format | |
| .alb | Development Files | Alpha Five Library | |
| .alc | Audio Files | Ableton Live Clip File | |
| .ald | Data Files | Dynamics AX Application Label Data File | |
| .alf | Data Files | ACT! Lookup File | |
| .alg | Audio Files | Cubase Multi Track Song File | |
| .ali | SAP Document Files | Dynamics AX Label Index File | |
| .all | Audio Files | Cubasis Project File | |
| .als | Audio Files | Ableton Live Set File | |
| .alt | Partially Downloaded Files | Dynamics AX Temporary File | |
| .alz | Compressed Files | ALZip Archive | |
| .amb | Data Files | AIMMS Model File | |
| .amf | Audio Files | Advanced Module File | |
| .amg | Audio Files | Ambisonics Soundfile Information Chunk File | |
| .aml | HTML Files | Microsoft Windows Vista Online Help File | |
| .amr | Compressed Audio Files | Adaptive Multi-Rate Codec File | |
| .ams | Configuration Files | Adobe Monitor Setup file | |
| .ams | Vector Graphics Files | NeroMix Image File | |
| .amsorm | Data Files | OnLine Ringman Auction Client File | |
| .amu | Data Files | PictureGear Studio Photo Album File | |
| .amxd | Audio Files | Ableton Max Patch File | |
| .an1 | Data Files | Street Atlas USA Draw File | |
| .an8 | Animation Files | Anim8or File | |
| .ani | Graphics Files | Windows Animated Cursor | |
| .anme | Data Files | Anime Studio Document | |
| .ans | Text Files | ANSI Text File | |
| .anx | Data Files | HotDocs Answer File | |
| .aob | Audio Files | DVD-Audio Audio Object File | |
| .aol | Partially Downloaded Files | America Online File | |
| .ap | Web Files | Active Page | |
| .ape | Winamp Files | Monkey's Audio Lossless Audio File | |
| .apf | Partially Downloaded Files | Adobe Profile File | |
| .aph | Data Files | Ability Album File | |
| .apk | Program Execution Files | Android Package File | |
| .apl | Audio Files | Monkey's Audio Track Information File | |
| .apl | GIS Files | ArcPad Layer File | |
| .apnx | Amazon eBook Files | Amazon Page Number Index File | |
| .app | Program Execution Files | Mac OS X Application | |
| .ar | Compressed Files | Unix Static Library | |
| .ar7 | Archive Files | AR7 Archive File | |
| .arc | Backup Files | Symbian OS Backup File | |
| .arch00 | Game Archive Files | F.E.A.R. Game Archive | |
| .arh | Compressed Files | ProTool Compressed Project File | |
| .aria | Audio Files | Chipsounds Sound File | |
| .ariax | Audio Files | Chipsounds XML Sound File | |
| .arsc | Development Files | Android Package Resource File | |
| .art | Raster Graphics Files | AOL Compressed Image File | |
| .as | Development Files | ActionScript File | |
| .asc | Development Files | ActionScript Communication File | |
| .ascii | Text Files | ASCII Text File | |
| .ascx | ASP Files | ASP.NET User Control File | |
| .asd | Backup Files | Word AutoSave File | |
| .ase | Configuration Files | Adobe Swatch Exchange File | |
| .asec | Mobile Files | Android Secure Application File | |
| .asf | Video Files | Advanced Systems Format File | |
| .ashbak | Backup Files | Ashampoo Backup Archive | |
| .ashprj | Data Files | Ashampoo Burning Studio Project | |
| .ashx | ASP Files | ASP.NET Web Handler File | |
| .asm | Development Files | Assembly Language Source Code File | |
| .asnd | Data Files | Adobe Sound Document | |
| .asp | Web Files | Active Server Page | |
| .aspx | ASP Files | Active Server Page Extended File | |
| .asr | Web Files | ActionScript Remote Document | |
| .ass | Multiple Use Files | Aegisub Advanced Substation Alpha File | |
| .ast | Configuration Files | Adobe Color Separations Table | |
| .ast | Spreadsheet Files | Ability Spreadsheet Template | |
| .asw | Raster Graphics Files | ACDSee Slideshow Wizard File | |
| .at3 | Audio Files | ATRAC3 Audio File | |
| .atf | Data Files | Axon Text File | |
| .atn | Configuration Files | Photoshop Actions File | |
| .atrac | Audio Files | Sony ATRAC Audio File | |
| .ats | Data Files | Advanced ETL Transformation Script | |
| .aty | Text Files | Association Type Placeholder | |
| .au | Audio Files | Audio File | |
| .au3 | Development Files | AutoIt v3 Script | |
| .aud | Audio Files | Video Game Compressed Audio File | |
| .aud | Audio Files | DTS Multi Channel Audio File | |
| .aup | Audio Files | Audacity Project File | |
| .ava | Adobe Files | AvaaBook eBook | |
| .avastlic | Multiple Use Files | Avast! License File | |
| .avc | Data Files | Kaspersky Virus Database | |
| .avhd | Microsoft Files | Hyper-V SnapShot File | |
| .avi | Digital Video Files | Audio Video Interleave File | |
| .avj | Data Files | AntiVir Job File | |
| .avl | GIS Files | ArcView Legend File | |
| .avp | Video Files | Avid Project File | |
| .avr | Audio Files | Audio Visual Research File | |
| .avs | Configuration Files | Avid Project Preferences File | |
| .aw | Data Files | Answer Wizard File | |
| .awb | Audio Files | AMR-WB Audio File | |
| .awdb | Data Files | Access Walker Database File | |
| .awg | Data Files | Activeworlds Object Group File | |
| .awm | Web Files | AllWebMenus Project File | |
| .awp | Text Files | Ability Write Template | |
| .awt | Text Files | AbiWord Template | |
| .aww | Document Files | Ability Write Document | |
| .ax | Filter Files | DirectShow Filter | |
| .axd | ASP Files | ASP.NET Web Handler File | |
| .axm | Video Files | AXMEDIS Object | |
| .axx | Encrypted Files | AxCrypt Encrypted File | |
| .ay | Audio Files | AY Chiptune File | |
| .azw | eBook Files | Amazon Kindle eBook File | |
| .azw1 | eBook Files | Amazon Topaz eBook | |
| .azw3 | Amazon eBook Files | Amazon KF8 eBook File | |
| .azw4 | Amazon eBook Files | Amazon Print Replica eBook | |
| .azz | Data Files | AZZ Cardfile Database File |