| .AME | Sage | Datatiedostot | ACT! E-mail System Library | Act! | Swiftpage, Inc. |
| .AMM | Bolide Software | Datatiedostot | All My Movies Database File | Bolide All My Movies | Bolide Software |
| .AMN | Microsoft Corporation | Datatiedostot | Aero Studio 2008 Menu Data | Aero Studio | Microsoft Corporation |
| .AMR | Open Source | Datatiedostot | Adaptive Multi-Rate Codec File | Apple QuickTime Player | Apple |
| .AMSM | Atom Park | Datatiedostot | Atomic Mail Sender Project | Atomic Mail Sender | Atom Park |
| .AMT | Planit Solutions, Inc. | Datatiedostot | Alphacam 3D Mill, 2D Mill Tool | Planit Alphacam | Planit Solutions, Inc. |
| .AMU | Sony | Datatiedostot | PictureGear Studio Photo Album File | PictureGear Studio | Sony |
| .AMW | Anark Corporation | Datatiedostot | Anark Media Studio Workspace | Anark Studio | Anark Corporation |
| .AN1 | DeLorme | Datatiedostot | Street Atlas USA Draw File | DeLorme Street Atlas USA | DeLorme |
| .AN8 | Steven Glanville | Datatiedostot | Anim8or File | Anim8or | Steven Glanville |
| .ANA | Cuylaerts Engineering | Datatiedostot | Analysis For Windows File | Analysis for Windows | Cuylaerts Engineering |
| .ANB | IBM | Datatiedostot | Analytical Chart | i2 Analyst's Notebook | IBM |
| .ANDROID | Unknown Developer | Datatiedostot | Android Readme File | Microsoft Notepad | Microsoft Corporation |
| .ANIME | Smith Micro Software | Datatiedostot | Anime Studio Document | Smith Micro Moho Debut 12 | Smith Micro Software |
| .ANKI | Damien Elmes | Datatiedostot | Anki Deck Data | Anki | Damien Elmes |
| .ANL | Planit Solutions, Inc. | Datatiedostot | Alphacam Nest List | Planit Alphacam | Planit Solutions, Inc. |
| .ANN | ABBYY | Datatiedostot | Lingvo Dictionary Annotation File | ABBYY Lingvo Dictionary | ABBYY |
| .ANS | Open Source | Datatiedostot | ANSI Text File | Microsoft Notepad | Microsoft Corporation |
| .ANT | Open Source | Datatiedostot | Radio Mobile Antenna Definition | Radio Mobile | Open Source |
| .ANYDVD | RedFox | Datatiedostot | AnyDVD Registration Key | AnyDVD HD | RedFox |
| .AOI | Open Source | Datatiedostot | Art Of Illusion 3D Scene | Art of Illusion | Open Source |
| .AOT | Novell, Inc. | Datatiedostot | Novell Application Object Template | NetWare | Novell, Inc. |
| .APC | Savvius, Inc. | Datatiedostot | AiroPeek Wireless Trace Capture File | AiroPeek | Savvius, Inc. |
| .APG | Unknown Developer | Datatiedostot | Ivana Animated GIF File | Unknown Software | Unknown Developer |
| .APH | Ability Plus Software | Datatiedostot | Ability Album File | Ability Office | Ability Plus Software |
| .APJ | The FreeBSD Community | Datatiedostot | FreeBSD File | FreeBSD | The FreeBSD Community |
| .APP | Nokia | Datatiedostot | Symbian OS Application | Symbian OS | Nokia |
| .APPLE | Apple | Datatiedostot | Apple AppleSingle Data File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .APPS | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .APX | Ability Plus Software | Datatiedostot | Ability Photopaint Studio Image | Ability Office | Ability Plus Software |
| .AQ | Incline Software | Datatiedostot | Ancestral Quest Genealogy Data | Ancestral Quest | Incline Software |
| .AQZ | Open Source | Datatiedostot | Amateur Radio Questionary Data File | AQZ File Parser for Java | Open Source |
| .ARCH | Unknown Developer | Datatiedostot | Illum Source Dotfiles File | Unknown Software | Unknown Developer |
| .ARH | Siemens AG | Datatiedostot | ProTool Compressed Project File | Siemens ProTool | Siemens AG |
| .ARMOURFONT | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .ARN | Microsoft Corporation | Datatiedostot | Autoruns Data File | Microsoft Autoruns | Microsoft Corporation |
| .ARS | Adobe Systems Incorporated | Datatiedostot | After Effects Render Settings File | Adobe After Effects | Adobe Systems Incorporated |
| .ART | Autodesk, Inc. | Datatiedostot | ArtCAM Model | ArtCAM | Autodesk, Inc. |
| .ARV | Microsoft Corporation | Datatiedostot | Microsoft Autoroute User Information File | Microsoft AutoRoute | Microsoft Corporation |
| .AS | Adobe Systems Incorporated | Datatiedostot | Adobe ActionScript File | Microsoft Notepad | Microsoft Corporation |
| .AS4 | askSam Systems | Datatiedostot | AskSam Backup File | askSam Systems SurfSaver | askSam Systems |
| .ASC | Symantec Corporation | Datatiedostot | PGP (Pretty Good Privacy) ASCII Armored File | Mozilla Thunderbird | Mozilla |
| .ASHPRJ | Ashampoo | Datatiedostot | Ashampoo Burning Studio Project | Ashampoo Burning Studio 18 | Ashampoo |
| .ASJ | Aldfaer Foundation | Datatiedostot | Aldfaer Genealogy File | Aldfaer | Aldfaer Foundation |
| .ASM | Open Source | Datatiedostot | Assembly Language Source Code File | Microsoft Notepad | Microsoft Corporation |
| .ASND | Adobe Systems Incorporated | Datatiedostot | Adobe Sound Document | Adobe Audition | Adobe Systems Incorporated |
| .ASQ | Unit4 | Datatiedostot | AGRESSO SQL Statement Data | AGRESSO SQL | Unit4 |
| .ASR | Adobe Systems Incorporated | Datatiedostot | ActionScript Remote Document | Adobe Dreamweaver | Adobe Systems Incorporated |
| .AST | Apple | Datatiedostot | ClarisWorks Assistant File | Apple AppleWorks | Apple |
| .AT2 | Adobe Systems Incorporated | Datatiedostot | Adobe Persuasion Auto Template | Aldus PhotoStyler | Adobe Systems Incorporated |
| .ATD | Planit Solutions, Inc. | Datatiedostot | Alphacam Lathe Drawing | Planit Alphacam | Planit Solutions, Inc. |
| .ATF | Molecular Devices | Datatiedostot | Axon Text File | Microsoft Excel | Microsoft Corporation |
| .ATM | E-on Software, Inc. | Datatiedostot | Vue Atmospheres File | E-on Vue | E-on Software, Inc. |
| .ATOMSVC | Microsoft Corporation | Datatiedostot | Atom Service Document | Microsoft Excel | Microsoft Corporation |
| .ATS | DB Software Laboratory | Datatiedostot | Advanced ETL Transformation Script | Advanced ETL Processor | DB Software Laboratory |
| .ATTR | Apple | Datatiedostot | iPhoto Attributes File | Apple iPhoto | Apple |
| .ATW | Unknown Developer | Datatiedostot | Attityd Survey Program Data | Unknown Software | Unknown Developer |
| .AUC | Jordysoft | Datatiedostot | AUC Database | Advanced URL Catalog | Jordysoft |
| .AUD | Interscape | Datatiedostot | Video Game Compressed Audio File | Command and Conquer | Interscape |
| .AUDIO | Apple | Datatiedostot | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .AUS | SourceForge | Datatiedostot | AutoREALM Symbols | AutoREALM | SourceForge |
| .AVA | Open Source | Datatiedostot | AvaaBook eBook | AvaaPlayer | Open Source |
| .AVC | Kaspersky Lab | Datatiedostot | Kaspersky Virus Database File | Kaspersky Anti-Virus | Kaspersky Lab |
| .AVG | AVG Technologies | Datatiedostot | AVG Antivirus Virus Database | AVG Antivirus | AVG Technologies |
| .AVH | Pioneer DJ Corporation | Datatiedostot | Pioneer AVH Firmware Update | Pioneer AVH | Pioneer DJ Corporation |
| .AVL | ESRI | Datatiedostot | ArcView Legend File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .AVP | Avid Technology | Datatiedostot | Avid Project File | Avid Media Composer | Avid Technology |
| .AVS | Adobe Systems Incorporated | Datatiedostot | Adobe Photoshop Variations File | Adobe Photoshop | Adobe Systems Incorporated |
| .AW | Microsoft Corporation | Datatiedostot | Answer Wizard File | Microsoft Excel | Microsoft Corporation |
| .AWF | Adobe Systems Incorporated | Datatiedostot | Adobe WorkFlow Workgroup Plugin | Adobe Creative Cloud | Adobe Systems Incorporated |
| .AWR | Lavasoft | Datatiedostot | Ad-Aware Reference File | Ad-Aware | Lavasoft |
| .AWX | ESRI | Datatiedostot | ArcIMS XML Project File | ArcIMS | ESRI |
| .AX2 | Apex Software | Datatiedostot | Ver. 2 Sketch File | Apex | Apex Software |
| .AXL | Wattle Software | Datatiedostot | XML File | MacroMates TextMate | MacroMates |
| .AXP | Canneverbe Limited | Datatiedostot | CDBurnerXP Audio Compilation File | Canneverbe CDBurnerXP | Canneverbe Limited |
| .AXS | Microsoft Corporation | Datatiedostot | ActiveX Script File | Microsoft Notepad | Microsoft Corporation |
| .AZK | Jonathan Forster | Datatiedostot | DMDX Output Document | DMDX | Jonathan Forster |
| .AZW3F | Amazon | Datatiedostot | Amazon eBook Metadata File | Amazon Kindle | Amazon |
| .AZZ | Antanas Zdramys | Datatiedostot | AZZ Cardfile Database File | AZZ Cardfile | Antanas Zdramys |
| .AZZX | Antanas Zdramys | Datatiedostot | Uncompressed AZZ Cardfile Data File | AZZ Cardfile | Antanas Zdramys |
| .A_T | Unknown Developer | Datatiedostot | Atrain File | Unknown Software | Unknown Developer |
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