| .33B | Unknown Developer | Entwicklerdateien | SYNETSIM Source Code | SYNETSIM | Unknown Developer |
| .3RF | Global Publishing Solutions | Entwicklerdateien | Advent 3B2 Extensions Script Cross Reference | Advanced Print Publisher (formerly Advent 3B2) | Global Publishing Solutions |
| .4DB | 4D, Inc | Entwicklerdateien | 4th Dimension Database Structure File | Unknown Software | Unknown Developer |
| .4DC | 4D, Inc | Entwicklerdateien | 4th Dimension Database Structure File | Unknown Software | Unknown Developer |
| .4FI | 4D, Inc | Entwicklerdateien | 4th Dimension Insider File | 4D SQL | 4D, Inc |
| .4GE | IBM | Entwicklerdateien | IBM Informix 4GL Compiled Source Code | IBM Informix | IBM |
| .4GL | IBM | Entwicklerdateien | Informix 4GL Language Source Code | IBM Informix | IBM |
| .4PK | Pitrinec | Entwicklerdateien | Perfect Keyboard Macro Set | Perfect Keyboard | Pitrinec |
| .4TH | Open Source | Entwicklerdateien | Forth Language File | Kate | KDE |
| .A | Open Source | Entwicklerdateien | Static Library | Microsoft Notepad | Microsoft Corporation |
| .A2W | Carnegie Mellon University | Entwicklerdateien | Alice World | Alice | Carnegie Mellon University |
| .A68 | Digital Equipment Corporation | Entwicklerdateien | PDP-10 Algol-68 Compiler Source | Unknown Software | Unknown Developer |
| .A86 | Eric Isaacson Software | Entwicklerdateien | A86 Assembly Language Source Code | A86/A386 | Eric Isaacson Software |
| .A8S | Steven Glanville | Entwicklerdateien | Anim8or Script | Anim8or | Steven Glanville |
| .ABA | Palm | Entwicklerdateien | Palm Address Book Archive | Palm Desktop | Palm |
| .ABC | Adobe Systems Incorporated | Entwicklerdateien | ActionScript Byte Code File | Adobe Flash Player | Adobe Systems Incorporated |
| .ABL | Ubisoft Blue Byte | Entwicklerdateien | ANNO 2070 Scenario Data | ANNO 2070 | Ubisoft Blue Byte |
| .ABO | Pierre Chambart, Jean-Christophe FILLIATRE and Sylvain Le Gall | Entwicklerdateien | Applix Builder File | Camomile (Library File) | Pierre Chambart, Jean-Christophe FILLIATRE and Sylvain Le Gall |
| .ACD | Sony Creative Software | Entwicklerdateien | ACID Project File | ACID XPress | Sony |
| .ACH | Rockwell Automation Inc. | Entwicklerdateien | RSLogix 5 Project File | RSLogix 5 | Rockwell Automation Inc. |
| .ACP | Alfresco Software, Inc. | Entwicklerdateien | Alfresco Content Package | Alfresco | Alfresco Software, Inc. |
| .ACTIONSCRIPT | Adobe Systems Incorporated | Entwicklerdateien | Adobe Flash ActionScript Data | Adobe Animate CC 2017 | Adobe Systems Incorporated |
| .ACU | Micro Focus International plc | Entwicklerdateien | Machine Independent COBOL Object File | ACUCOBOL-GT | Micro Focus International plc |
| .AD2 | Unknown Developer | Entwicklerdateien | ADPCM 2-bit Compressed Voice | Awave Studio | FMJ-Software |
| .ADA | Open Source | Entwicklerdateien | Ada Source Code | Notepad++ | Don Ho |
| .ADB | Open Source | Entwicklerdateien | Ada Body File | MacroMates TextMate | MacroMates |
| .ADIUMSCRIPTS | Adam Iser | Entwicklerdateien | Adium AppleScripts File | Adium | Open Source |
| .ADS | Open Source | Entwicklerdateien | Ada Specification File | MacroMates TextMate | MacroMates |
| .AEM | Planit Solutions, Inc. | Entwicklerdateien | Alphacam Wire EDM Parameter Macro | Planit Alphacam | Planit Solutions, Inc. |
| .AGC | John Bridges | Entwicklerdateien | AfterGRASP Compiled Script | AfterGRASP | Open Source |
| .AGI | Digium Inc. | Entwicklerdateien | Asterisk Gateway Interface File | Asterisk | Digium Inc. |
| .AGO | Soft Machines | Entwicklerdateien | Autolog Script | AutoLog | Soft Machines |
| .AGP | RL Vision | Entwicklerdateien | ArtGem Project File | ArtGem | RL Vision |
| .AGS | John Bridges | Entwicklerdateien | AfterGRASP Script File | AfterGRASP | Open Source |
| .AIML | Richard S. Wallace | Entwicklerdateien | Artificial Intelligence Markup Language | Notepad++ | Don Ho |
| .AIO | IBM | Entwicklerdateien | APL Transfer Format File | IBM APL | IBM |
| .AJB | Planit Solutions, Inc. | Entwicklerdateien | Alphacam Water Jet VB Macro | Microsoft Visual Basic | Microsoft Corporation |
| .AJM | Planit Solutions, Inc. | Entwicklerdateien | Alphacam Water Jet Parameter Macro | Planit Alphacam | Planit Solutions, Inc. |
| .AKP | Propellerhead | Entwicklerdateien | Akai Sampler File | ReCycle | Propellerhead |
| .ALB | Alpha Software | Entwicklerdateien | Alpha Five Library | Alpha Anywhere - Alpha Software | Alpha Software |
| .ALM | Alpha Software | Entwicklerdateien | Alpha Five Library | Alpha Anywhere - Alpha Software | Alpha Software |
| .ALP | AnyLogic | Entwicklerdateien | AnyLogic Project File | AnyLogic | AnyLogic |
| .ALX | BlackBerry | Entwicklerdateien | BlackBerry Application Loader XML File | BlackBerry Desktop Software | BlackBerry |
| .AM | GNU Operating System | Entwicklerdateien | Automake Makefile Template | Automake | GNU Operating System |
| .AM3 | Indigo Rose | Entwicklerdateien | AutoPlay Media Studio 3.0 Project | AutoPlay Media Studio | Indigo Rose |
| .AM4 | Indigo Rose | Entwicklerdateien | AutoPlay Media Studio 4 Project File | AutoPlay Media Studio | Indigo Rose |
| .AM5 | Indigo Rose | Entwicklerdateien | AutoPlay Media Studio 5 Project File | AutoPlay Media Studio | Indigo Rose |
| .AM6 | Indigo Rose | Entwicklerdateien | AutoPlay Media Studio 6 Project | AutoPlay Media Studio | Indigo Rose |
| .AML | Intel Corporation | Entwicklerdateien | ACPI Machine Language File | DSDTSE | otRock |
| .AMW | Anark Corporation | Entwicklerdateien | Anark Media Studio Workspace | Anark Studio | Anark Corporation |
| .ANDROIDPROJ | Microsoft Corporation | Entwicklerdateien | Microsoft Visual Studio Android Project | Microsoft Visual Studio | Microsoft Corporation |
| .ANM | Unknown Developer | Entwicklerdateien | 3D Animation File | CRYENGINE | Crytek |
| .APA | Rockwell Automation Inc. | Entwicklerdateien | RSView Development Project Archive | Rockwell Automation RSView Studio or RSView ME | Rockwell Automation Inc. |
| .APB | Planit Solutions, Inc. | Entwicklerdateien | Alphacam Punch VB Macro | Planit Alphacam | Planit Solutions, Inc. |
| .APM | Adobe Systems Incorporated | Entwicklerdateien | Aldus Placeable Metafile Image | GIMP | The GIMP Development Team |
| .APPX | Microsoft Corporation | Entwicklerdateien | Windows 8 App Package | Microsoft Windows 8 | Microsoft Corporation |
| .APPXMANIFEST | Microsoft Corporation | Entwicklerdateien | Windows Store App Source Manifest | Microsoft Visual Studio | Microsoft Corporation |
| .APR | ESRI | Entwicklerdateien | ArcView Project File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .APS | Microsoft Corporation | Entwicklerdateien | Visual C++ Resource File | Microsoft Visual C++ | Microsoft Corporation |
| .AP_ | Google | Entwicklerdateien | ADT Android Developer Package | 7-Zip | Igor Pavlov |
| .ARQ | BMC | Entwicklerdateien | BSM Action Request System Client Macro | BMC | BMC |
| .ARR | Lemkesoft | Entwicklerdateien | Amber Graphic File | Lemkesoft GraphicConverter | Lemkesoft |
| .ART | Autodesk, Inc. | Entwicklerdateien | ArtCAM Model | ArtCAM | Autodesk, Inc. |
| .ARY | Hewlett-Packard | Entwicklerdateien | SmartStart Scripting Toolkit Data | SmartStart | Hewlett-Packard |
| .AS | Adobe Systems Incorporated | Entwicklerdateien | Adobe ActionScript File | Microsoft Notepad | Microsoft Corporation |
| .AS3 | IBM | Entwicklerdateien | APL*PLUS Source Code File | IBM APL | IBM |
| .ASC | Symantec Corporation | Entwicklerdateien | PGP (Pretty Good Privacy) ASCII Armored File | Mozilla Thunderbird | Mozilla |
| .ASI | Borland | Entwicklerdateien | ASsembler Include | Asi Loader | Interscape |
| .ASM | Open Source | Entwicklerdateien | Assembly Language Source Code File | Microsoft Notepad | Microsoft Corporation |
| .ASO | Adobe Systems Incorporated | Entwicklerdateien | ActionScript Object | Adobe Creative Cloud | Adobe Systems Incorporated |
| .ASX | Microsoft Corporation | Entwicklerdateien | Microsoft ASF Redirector File | VLC Media Player | VideoLAN |
| .ASZ | Open Source | Entwicklerdateien | AlphaControls Skin Package | AlphaControls | Open Source |
| .ATG | Unknown Developer | Entwicklerdateien | Netmino File | Netmino | Unknown Developer |
| .ATP | Planit Solutions, Inc. | Entwicklerdateien | Alphacam Lathe Post File | Planit Alphacam | Planit Solutions, Inc. |
| .AU3 | Jonathan Bennett | Entwicklerdateien | AutoIt V3 Script | AutoIt | Jonathan Bennett |
| .AUT | Jonathan Bennett | Entwicklerdateien | AutoIt Script File | AutoIt | Jonathan Bennett |
| .AWK | Free Software Foundation | Entwicklerdateien | AWK Script | Apple TextEdit | Apple |
| .AWL | Lavasoft | Entwicklerdateien | Ad-Aware Language Data | Ad-Aware | Lavasoft |
| .AXB | Alpha Software | Entwicklerdateien | Alpha Five Xbasic Script | Alpha Five | Alpha Software |
| .AXE | Microsoft Corporation | Entwicklerdateien | AutoRoute Map File | Microsoft AutoRoute | Microsoft Corporation |
| .AXF | ARM Ltd | Entwicklerdateien | ARM RealView Compiler Object | RealView Development Suite | ARM Ltd |
| .AXS | Microsoft Corporation | Entwicklerdateien | ActiveX Script File | Microsoft Notepad | Microsoft Corporation |
| .B | Rockstar Games | Entwicklerdateien | Grand Theft Auto 3 Saved Game File | Grand Theft Auto III | Rockstar Games |
| .B2D | Guilect | Entwicklerdateien | Brutus2D Source Code File | Brutus2D | Guilect |
| .B32 | Microsoft Corporation | Entwicklerdateien | MS-DOS BCC Data | MS-DOS | Microsoft Corporation |
| .BAS | SoftMaker Software | Entwicklerdateien | BASIC Source Code File | Softmaker Office | SoftMaker Software |
| .BASH | Apple | Entwicklerdateien | Unix Bourne Shell (Bash) Script | Notepad++ | Don Ho |
| .BAZ | Unknown Developer | Entwicklerdateien | Acomba Accounting Suite Backup | Acomba Accounting Suite | ACCEO |
| .BB | Blitz Research | Entwicklerdateien | Blitz Source Code File | BlitzMax | Blitz Research |
| .BBC | Richard T. Russell | Entwicklerdateien | BBC BASIC Data File | BBC BASIC for Windows | Richard T. Russell |
| .BBF | Open Source | Entwicklerdateien | ScriptBasic Compiled Binary File | ScriptBasic | Open Source |
| .BCC | Broderbund | Entwicklerdateien | Calendar Creator File | Calendar Creator | Broderbund |
| .BCP | Blackmagic Design | Entwicklerdateien | BlackMagic Custom Palette | Adobe Photoshop | Adobe Systems Incorporated |
| .BDSPROJ | Embarcadero Technologies | Entwicklerdateien | Borland Developer Studio Project | Borland C++ | Micro Focus International plc |
| .BET | Birger Møller-Pedersen and Kristen Nygaard | Entwicklerdateien | BETA Source File | Notepad++ | Don Ho |
| .BETA | Birger Møller-Pedersen and Kristen Nygaard | Entwicklerdateien | Beta Programming Language Source Code | Beta Programming Language | Birger Møller-Pedersen and Kristen Nygaard |
| .BFO | Unknown Developer | Entwicklerdateien | GT Nexus PDF Template | GT Nexus | Unknown Developer |
| .BGM | Tom Mulgrew | Entwicklerdateien | Basic4GL 3D Object | Basic4GL | Tom Mulgrew |
| .BHS | Microsoft Corporation | Entwicklerdateien | Rise Of Nations Script | Rise Of Nations | Big Huge Games |
| .BIZDESIGN | Actuate Corporation | Entwicklerdateien | BusinessReport Design File | BusinessReport | Actuate Corporation |
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