| .253 | Alcatel-Lucent S.A. | Settings Files | Speed Touch DSL Modem Firmware Update | Unknown Software | Unknown Developer |
| .303 | Unknown Developer | Settings Files | Seq-303 Settings Files | Seq-303 | Metaphoric Software |
| .310 | Tri-Sen Systems | Settings Files | Tri-Sen TS310 Controller Configuration File | Tri-Sen TS310 | Tri-Sen Systems |
| .3CN | Microsoft Corporation | Settings Files | 3D Movie Maker Scene Data | 3D Movie Maker | Microsoft Corporation |
| .3FX | Corel | Settings Files | Corel Chart 3D Effect | CorelDRAW Graphics Suite | Corel |
| .3O3 | Metaphoric Software | Settings Files | 3O3 Settings Files | Seq-303 | Metaphoric Software |
| .3TH | Microsoft Corporation | Settings Files | 3D Movie Maker Thumbnail Data File | 3D Movie Maker | Microsoft Corporation |
| .426 | Alcatel-Lucent S.A. | Settings Files | Firewall Firmware Update | Unknown Software | Unknown Developer |
| .4CM | Pitrinec | Settings Files | ClickyMouse Macro Set | ClickyMouse | Pitrinec |
| .4TW | Pitrinec | Settings Files | Macro Toolworks Macro Set | Macro Toolworks | Pitrinec |
| .521 | Murry State University | Settings Files | Murray State University Trojan Ring Configuration File | Trojan Ring | Murry State University |
| .89K | Texas Instruments, Inc. | Settings Files | TI-89 Application File | TI-89 | Texas Instruments, Inc. |
| .89S | Texas Instruments, Inc. | Settings Files | TI-89 Application File | TI-89 | Texas Instruments, Inc. |
| .A2M | TallStick Software | Settings Files | TS-AudioToMIDI Settings File | TS-AudioToMIDI | TallStick Software |
| .AAP | Heikki Ylinen | Settings Files | Apollo Advanced Playlist | Apollo | ApolloDB |
| .AAWDEF | Lavasoft | Settings Files | Ad-Aware Definitions File | Ad-Aware | Lavasoft |
| .ABS | ComponentAce | Settings Files | Absolute Database File | ComponentAce Absolute Database | ComponentAce |
| .ACB | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Color Book File | Adobe Illustrator CC | Adobe Systems Incorporated |
| .ACF | Valve | Settings Files | Steam Application Cache File | Valve Steam | Valve |
| .ACO | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Color Swatch File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .ACS4 | Artem Izmaylov | Settings Files | AIMP Skin File | AIMP | Artem Izmaylov |
| .ACV | Adobe Systems Incorporated | Settings Files | Photoshop Curves File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .ACW | Microsoft Corporation | Settings Files | Windows Accessibility Wizard File | Microsoft Windows Accessibility Wizard | Microsoft Corporation |
| .ADIUMMENUBARICONS | Adam Iser | Settings Files | Adium Menu Bar Icon File | Adium | Open Source |
| .ADIUMMESSAGESTYLE | Adam Iser | Settings Files | Adium Message Style Settings | Adium | Open Source |
| .ADIUMSOUNDSET | The Adium team | Settings Files | Adium Sound Set File | Adium | Open Source |
| .ADM | Microsoft Corporation | Settings Files | Administrative Template File | Microsoft Group Policy Object Editor | Microsoft Corporation |
| .ADO | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Duotone Options File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AES | Open Source | Settings Files | AES Crypt Encrypted File | Packetizer AES Crypt | Open Source |
| .AFW | iGrafx | Settings Files | Micrografx FlowCharter Work Area Data | iGrafx Designer | Corel |
| .AGDB | ANSYS, Inc. | Settings Files | ANSYS DesignSpace Data | ANSYS DesignSpace | ANSYS, Inc. |
| .AGG | New World Computing | Settings Files | Bulk Data File | Heroes of Might & Magic III | Ubisoft |
| .AHL | Open Source | Settings Files | eMule Metadata | eMule | Open Source |
| .AHS | Adobe Systems Incorporated | Settings Files | Adobe Halftone Screen File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AHU | Adobe Systems Incorporated | Settings Files | Adobe Photoshop HSL File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AIP | Adobe Systems Incorporated | Settings Files | Illustrator Plug-in | Adobe Illustrator CC | Adobe Systems Incorporated |
| .AIT | Adobe Systems Incorporated | Settings Files | Adobe Illustrator Template | Adobe Illustrator CC | Adobe Systems Incorporated |
| .AIU | Caphyon | Settings Files | Advanced Installer Updates Configuration File | Advanced Installer | Caphyon |
| .ALL | Steinberg | Settings Files | Cubase Project | Steinberg Cubase | Steinberg |
| .ALV | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Levels File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .ALX | BlackBerry | Settings Files | BlackBerry Application Loader XML File | BlackBerry Desktop Software | BlackBerry |
| .AMP | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Curves Map File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AMS | Adobe Systems Incorporated | Settings Files | Adobe Monitor Setup File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .ANC | Canon Inc. | Settings Files | Canon Computer Pattern Maker Color Pattern List | Canon Raw Codec | Canon Inc. |
| .ANV | Birch Grove Software, Inc. | Settings Files | ActivTrak Net View File | ActivTrak | Birch Grove Software, Inc. |
| .AOM | Adobe Systems Incorporated | Settings Files | After Effects Output Module | Adobe After Effects | Adobe Systems Incorporated |
| .APC | Savvius, Inc. | Settings Files | AiroPeek Wireless Trace Capture File | AiroPeek | Savvius, Inc. |
| .API | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Inks File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .APM | Adobe Systems Incorporated | Settings Files | Aldus Placeable Metafile Image | GIMP | The GIMP Development Team |
| .APPCONTENT-MS | Microsoft Corporation | Settings Files | Microsoft Windows Application Content | Microsoft Windows 8 | Microsoft Corporation |
| .APPLICATION | Microsoft Corporation | Settings Files | ClickOnce Deployment Manifest File | Microsoft .NET Framework | Microsoft Corporation |
| .APPREF-MS | Microsoft Corporation | Settings Files | Microsoft Application Reference File | Microsoft ClickOnce | Microsoft Corporation |
| .ARG | Autodesk, Inc. | Settings Files | AutoCAD Profile | Autodesk AutoCAD | Autodesk, Inc. |
| .ARL | AOL | Settings Files | AOL Organizer File | AOL Organizer | AOL |
| .ARP | ElcomSoft | Settings Files | Advanced RAR Password Recovery Setup | Advanced Archive Password Recovery | ElcomSoft |
| .ARS | Adobe Systems Incorporated | Settings Files | After Effects Render Settings File | Adobe After Effects | Adobe Systems Incorporated |
| .ASE | Adobe Systems Incorporated | Settings Files | Adobe Swatch Exchange File | Adobe Illustrator CC | Adobe Systems Incorporated |
| .ASK | askSam Systems | Settings Files | AskSam Database | askSam | Softonic Corporate |
| .ASL | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Style | Adobe Photoshop | Adobe Systems Incorporated |
| .ASP | Microsoft Corporation | Settings Files | Active Server Page | Mozilla Firefox | Mozilla |
| .AST | Apple | Settings Files | ClarisWorks Assistant File | Apple AppleWorks | Apple |
| .ASV | MakeMusic, Inc. | Settings Files | Finale Auto-save File | Finale | MakeMusic, Inc. |
| .ASW | ACD Systems | Settings Files | ACDSee Slideshow Wizard File | ACD Systems ACDSee | ACD Systems |
| .ASWCS | Avast Software | Settings Files | Avast! Compressed Skin File | Avast Antivirus | Avast Software |
| .ASWS | Avast Software | Settings Files | Avast! Skin File | Avast Antivirus | Avast Software |
| .ATC | Autodesk, Inc. | Settings Files | AutoCAD Tool Catalog File | Autodesk AutoCAD Civil 3D | Autodesk, Inc. |
| .ATF | Molecular Devices | Settings Files | Axon Text File | Microsoft Excel | Microsoft Corporation |
| .ATH | Dell Boomi | Settings Files | Alienware AlienFX Theme File | Microsoft XML Notepad | Microsoft Corporation |
| .ATN | Adobe Systems Incorporated | Settings Files | Photoshop Actions File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AUTOCONF | The Open Group | Settings Files | Autoconfiguration File | Unix | AT&T Labs |
| .AUX | Interscape | Settings Files | LaTeX Auxiliary File | MiKTeX | Christian Schenk |
| .AVE | Avid Technology | Settings Files | Avid User File | Avid Media Composer | Avid Technology |
| .AVS | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Variations File | Adobe Photoshop | Adobe Systems Incorporated |
| .AWE | Adobe Systems Incorporated | Settings Files | Adobe Acrobat Bookmark XML Data | Adobe Creative Cloud | Adobe Systems Incorporated |
| .AWL | Lavasoft | Settings Files | Ad-Aware Language Data | Ad-Aware | Lavasoft |
| .AXC | Microsoft Corporation | Settings Files | Microsoft Dynamics AX Configuration | Microsoft Dynamics AX | Microsoft Corporation |
| .AXL | Wattle Software | Settings Files | XML File | MacroMates TextMate | MacroMates |
| .AXP | Canneverbe Limited | Settings Files | CDBurnerXP Audio Compilation File | Canneverbe CDBurnerXP | Canneverbe Limited |
| .AXT | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Extract File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .AZD | Amazon | Settings Files | Amazon Software Download File | Amazon Software Downloader | Amazon |
| .BASIN | U.S. Army Corps of Engineers | Settings Files | HEC-HMS Basin Model Settings File | HEC-HMS | U.S. Army Corps of Engineers |
| .BAU | Sun Microsystems | Settings Files | Apache OpenOffice AutoText File | Apache OpenOffice | Apache Software Foundation |
| .BBD | Xilinx, Inc. | Settings Files | Xilinx Black Box Definition | Xilinx CORE Generator System | Xilinx, Inc. |
| .BCP | Blackmagic Design | Settings Files | BlackMagic Custom Palette | Adobe Photoshop | Adobe Systems Incorporated |
| .BCS | The Wavelength | Settings Files | Batch Compiler Specification File | Batch Compiler | The Wavelength |
| .BCW | Micro Focus International plc | Settings Files | Borland C++ Workspace Data | Borland C++ | Micro Focus International plc |
| .BDB2 | Brainmaster Technologies | Settings Files | BrainMaster Settings | BrainAvatar | Brainmaster Technologies |
| .BDF | Willowsoft Creek Software | Settings Files | Backup Definition File | Backup Made Simple | Willowsoft Creek Software |
| .BEX | Symantec Corporation | Settings Files | PGP Binary Extracted Public Key | Pretty Good Privacy (PGP) | Symantec Corporation |
| .BFD | Open Source | Settings Files | Linux BFD Rules Configuration Data | Linux | Open Source |
| .BGI | Microsoft Corporation | Settings Files | BgInfo Configuration File | BgInfo | Microsoft Corporation |
| .BKS | Microsoft Corporation | Settings Files | NTBackup Settings File | Microsoft Windows NT Backup - Restore Utility | Microsoft Corporation |
| .BLOB | Valve | Settings Files | Valve Steam Archive | Steam | Valve |
| .BLT | AOL | Settings Files | AIM Buddy List | AOL Instant Messenger (AIM) | AOL |
| .BLW | Adobe Systems Incorporated | Settings Files | Adobe Photoshop Black And White Presets File | Adobe Photoshop CC | Adobe Systems Incorporated |
| .BMM | Isao Maruoka | Settings Files | Tacmi Pixia Palette | Pixia | Isao Maruoka |
| .BOOT | Flexera Software | Settings Files | InstallShield Boot File | InstallShield | Flexera Software |
| .BRIDGESORT | Adobe Systems Incorporated | Settings Files | Adobe Bridge Cabinet | Adobe Bridge CC | Adobe Systems Incorporated |
| .BSH | Open Source | Settings Files | BeanShell Script | Microsoft Notepad | Microsoft Corporation |
| .BSI | Webteh | Settings Files | BSPlayer Configuration File | BS.player | Webteh |
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