| .A-0 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .A021 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .A1J | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .A2 | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .A3 | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .A349 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .A4J | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .A68 | Digital Equipment Corporation | Developer Files | PDP-10 Algol-68 Compiler Source | Unknown Software | Unknown Developer |
| .A8 | Cubicomp | Raster Image Files | Cubicomp PictureMaker 3D Animation Data | Unknown Software | Unknown Developer |
| .AA48 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ABB | Unknown Developer | Data Files | AlphaBB Data | Unknown Software | Unknown Developer |
| .AC7 | National Instruments | Data Files | SPICE AC/Frequency Domain Output File | Unknown Software | Unknown Developer |
| .ACT | Bell Labs | Audio Files | ADPCM Compressed Audio File | Unknown Software | Unknown Developer |
| .ACTBIN | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ACUTC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ADRESSES | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .AEG | Unknown Developer | Uncommon Files | Netmino File | Netmino | Unknown Developer |
| .AFAE | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .AFX FILE EXTENSION | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .AHF | Anadigm | Data Files | AnadigmDesigner ASCII Code | Unknown Software | Unknown Developer |
| .AHQ | Unknown Developer | Plugin Files | AudioHQ Plug-in Module | Unknown Software | Unknown Developer |
| .AHR0CDOVL2 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .AIN | Valve | Game Files | Source Engine Compiled AI Nodegraph File | Multi Unpacker | Unknown Developer |
| .AINSO | Unknown Developer | Data Files | CRYSTALS Chemical Crystallogaphy File | CRYSTALS | Unknown Developer |
| .AJ0 | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .AJO | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .AK | Unknown Developer | Compressed Files | Audio Utility Tuningwrench Compressed File | Unknown Software | Unknown Developer |
| .ALBM | Hewlett-Packard | Raster Image Files | HP Photo Printing Software Album File | Unknown Software | Unknown Developer |
| .ALDRIN | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .APG | Unknown Developer | Graphic Files | Ivana Animated GIF File | Unknown Software | Unknown Developer |
| .APN | Alpine Electronics | 3D Image Files | Alpine Wallpaper | Unknown Software | Unknown Developer |
| .APPS | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .ARCH | Unknown Developer | Data Files | Illum Source Dotfiles File | Unknown Software | Unknown Developer |
| .ARMOURFONT | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .ASXP | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .AT | Unknown Developer | Uncommon Files | Rescue Disk File | Unknown Software | Unknown Developer |
| .ATG | Unknown Developer | Uncommon Files | Netmino File | Netmino | Unknown Developer |
| .ATOS | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ATW | Unknown Developer | Data Files | Attityd Survey Program Data | Unknown Software | Unknown Developer |
| .AUDIO | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .AVH | Pioneer DJ Corporation | Data Files | Pioneer AVH Firmware Update | OXE CCTV DVR Recorder | Unknown Developer |
| .AW_ | Unknown Developer | Compressed Files | Midiprg Quartz Sets Compressed File | Unknown Software | Unknown Developer |
| .AY | Richard Bannister | Audio Files | AY Chiptune File | Micro Speccy | Unknown Developer |
| .AYA | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .AYE | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .AZA | Unknown Developer | Compressed Files | QazaR Archive Compressed File | QazaR | Unknown Developer |
| .AZX | Unknown Developer | Audio Files | ZX Audio File Format | Unknown Software | Unknown Developer |
| .A_T | Unknown Developer | Data Files | Atrain File | Unknown Software | Unknown Developer |
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