| .ELF | Nintendo | System Files | Nintendo Wii Game File | Dolphin (emulator) | Dolphin Emulator Project |
| .ELL | Advanced Micro Devices, Inc. | System Files | AMD ATI Radeon Video Driver | ATI Multimedia Center | Advanced Micro Devices, Inc. |
| .ESN | Epic Games | System Files | Unreal Engine Language Localization | Unreal Tournament | Epic Games |
| .ETL | Microsoft Corporation | System Files | Microsoft Event Trace Log File | Microsoft Event Viewer | Microsoft Corporation |
| .EVT | Microsoft Corporation | System Files | Microsoft Windows 2000 And XP Event Log | Microsoft Event Viewer | Microsoft Corporation |
| .EVTX | Microsoft Corporation | System Files | Windows 7 Event Log File | Microsoft Event Viewer | Microsoft Corporation |
| .FEI | Geoworks Ensemble | System Files | Geoworks Dependency Information File | GEOS (Graphic Environment Operating System) | Geoworks Ensemble |
| .FFA | Microsoft Corporation | System Files | Find Fast Status File | Microsoft Outlook | Microsoft Corporation |
| .FFO | Microsoft Corporation | System Files | Find Fast Document Properties Cache | Microsoft Outlook | Microsoft Corporation |
| .FFX | Adobe Systems Incorporated | System Files | After Effects Preset File | Adobe After Effects | Adobe Systems Incorporated |
| .FID | Microsoft Corporation | System Files | Windows Indexing Service File | Microsoft Windows | Microsoft Corporation |
| .FLG | Larry Short, Mick Amadio and Puppy community | System Files | Puppy Linux Partition Flag File | Puppy Linux | Larry Short, Mick Amadio and Puppy community |
| .FOLDER | Microsoft Corporation | System Files | Microsoft Windows Explorer Folder File | Microsoft Windows | Microsoft Corporation |
| .FPBF | Apple | System Files | Mac OS X Burn Folder | Apple OS X | Apple |
| .FS | Microsoft Corporation | System Files | Visual F# Source File | Microsoft Visual Studio | Microsoft Corporation |
| .FTG | Microsoft Corporation | System Files | Full Text Group | Microsoft Windows Help | Microsoft Corporation |
| .FTS | Microsoft Corporation | System Files | Full Text Search | Microsoft Windows Help | Microsoft Corporation |
| .FX | Microsoft Corporation | System Files | Direct3D Effects File | Microsoft Visual Studio | Microsoft Corporation |
| .GID | Microsoft Corporation | System Files | Windows Help Global Index File | Microsoft Windows Help | Microsoft Corporation |
| .GMMP | Microsoft Corporation | System Files | WCS Gamut Map Model Profile | Microsoft Windows | Microsoft Corporation |
| .GR2 | Larian Studios | System Files | Divinity: Original Sin Game Data | Divinity: Original Sin | Larian Studios |
| .GR3 | Orchid Technology KK | System Files | Graphics Device Driver | Unknown Software | Unknown Developer |
| .GRB | Microsoft Corporation | System Files | MS-DOS Shell Monitor Data | MS-DOS | Microsoft Corporation |
| .GROUP | Microsoft Corporation | System Files | Windows Contacts Group File | Microsoft Windows Contacts | Microsoft Corporation |
| .GRP | Blizzard Entertainment Inc. | System Files | StarCraft Graphics Group File | StarCraft | Blizzard Entertainment Inc. |
| .H1S | Microsoft Corporation | System Files | Windows Assistance Platform Help File | Microsoft Windows | Microsoft Corporation |
| .HAM | Interplay Entertainment | System Files | Descent 2 Resource File | Interplay Descent 2 | Interplay Entertainment |
| .HCD | Samsung Electronics | System Files | Samsung Android Firmware File | Google Android | Google |
| .HDMP | Microsoft Corporation | System Files | Windows Heap Dump | Microsoft Windows | Microsoft Corporation |
| .HELP | Apple | System Files | Mac OS X Help Book | macOS | Apple |
| .HHC | Microsoft Corporation | System Files | HTML Help Table Of Contents | Microsoft HTML Help Workshop | Microsoft Corporation |
| .HHK | Microsoft Corporation | System Files | HTML Help Index | Microsoft HTML Help Workshop | Microsoft Corporation |
| .HIV | Microsoft Corporation | System Files | Windows Registry Hive File | Microsoft Windows | Microsoft Corporation |
| .HLP | Microsoft Corporation | System Files | Windows Help File | Microsoft Windows | Microsoft Corporation |
| .HPJ | Microsoft Corporation | System Files | Help Project File | Adobe RoboHelp | Adobe Systems Incorporated |
| .HSH | Microsoft Corporation | System Files | Windows Catalog Search Index File | Microsoft Windows | Microsoft Corporation |
| .HTT | Microsoft Corporation | System Files | Hypertext Template File | Microsoft Windows | Microsoft Corporation |
| .HTW | Microsoft Corporation | System Files | IIS Webhits Template | Microsoft IIS | Microsoft Corporation |
| .ICL | Microsoft Corporation | System Files | Windows Icon Library File | Microsoft Windows | Microsoft Corporation |
| .ICO | The GIMP Development Team | System Files | Icon File | GIMP | The GIMP Development Team |
| .IDENTIFIER | Microsoft Corporation | System Files | Windows Zone Identifier File | Microsoft Windows | Microsoft Corporation |
| .IDI | Hewlett-Packard | System Files | EVA Controller Event Log | Enterprise Virtual Array | Hewlett-Packard |
| .IME | Microsoft Corporation | System Files | Windows Input Method Editor File | Microsoft Windows | Microsoft Corporation |
| .IMG3 | Apple | System Files | Apple iOS Img3 Encrypted Or Signed Container | Apple iTunes | Apple |
| .INS | Open Source | System Files | LaTeX Installer Script | Microsoft Notepad | Microsoft Corporation |
| .ION | Open Source | System Files | File Description File | Microsoft Notepad | Microsoft Corporation |
| .IPE | Microsoft Corporation | System Files | .ini And Win.ini Backup For Wacom Pen System | Unknown Software | Unknown Developer |
| .IPOD | Open Source | System Files | Rockbox Firmware File | Rockbox Utility | Open Source |
| .IPTHEME | Stardock Corporation | System Files | IconPackager Raw Theme File | Stardock Icon Packager | Stardock Corporation |
| .ITS | Open Source | System Files | Impulse Tracker Sample | CocoModX | Open Source |
| .IUS | Shanghai InfoTM Microelectronics Co., Ltd. | System Files | InfoTMIC Firmware Update File | Unknown Software | Unknown Developer |
| .JLB | Microsoft Corporation | System Files | PAC Mate BX Keyboard Driver | Windows Mobile | Microsoft Corporation |
| .JOB | Metamation | System Files | MetaCAM Nest Job File | MetaCAM Nesting | Metamation |
| .JPN | Microsoft Corporation | System Files | Windows Japanese Noise-Word List File | Microsoft Notepad | Microsoft Corporation |
| .KBD | Autodesk, Inc. | System Files | 3ds Max Keyboard Shortcuts File | Autodesk 3ds Max | Autodesk, Inc. |
| .KEXT | Apple | System Files | Mac OS X Kernel Extension | Apple OS X | Apple |
| .KEY | Unknown Developer | System Files | License/ Encrypted Security Key File | Avira Antivirus Pro 2016 | Avira Operations GmbH & Co. KG. |
| .KO | Open Source | System Files | Linux Kernel Module File | Linux | Open Source |
| .KOR | Epic Games | System Files | Unreal Engine Language Localization | Unreal Tournament | Epic Games |
| .KPD | Kaspersky Lab | System Files | Kaspersky Lab Application Description | Kaspersky Anti-Virus | Kaspersky Lab |
| .KRM | Kenwood Corporation | System Files | Kenwood Firmware Data | Unknown Software | Unknown Developer |
| .KS | Debian | System Files | Kickstart File | MIC2 | Debian |
| .KSS | FabTrol Systems | System Files | FabTrol MRP Template | FabTrol | FabTrol Systems |
| .LAN | ESRI (Environmental Systems Research Institute) | System Files | ERDAS LAN File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .LBR | Dag Agren, Circlesoft | System Files | LU Library Archive | The Unarchiver | Dag Agren, Circlesoft |
| .LGX | Microsoft Corporation | System Files | Microsoft Windows Received Message Data | Microsoft Windows | Microsoft Corporation |
| .LIBRARY-MS | Microsoft Corporation | System Files | Windows Library Description File | Microsoft Windows | Microsoft Corporation |
| .LNK | Microsoft Corporation | System Files | Windows File Shortcut | Microsoft Windows | Microsoft Corporation |
| .LOW | Digital Equipment Corporation | System Files | PDP-10 Low Segment Of A Two-segment Program | Unknown Software | Unknown Developer |
| .LPD | GNU Project | System Files | LPD Daemon Print Permissions File | Vim | Bram Moolenaar |
| .LST | Unknown Developer | System Files | Data List | LibreOffice | The Document Foundation |
| .MAN | Unknown Developer | System Files | Unix Manual | LibreOffice | The Document Foundation |
| .MANIFEST | Microsoft Corporation | System Files | Windows Application Manifest File | Microsoft Notepad | Microsoft Corporation |
| .MAPIMAIL | Microsoft Corporation | System Files | Send To Mail Recipient | Microsoft Windows | Microsoft Corporation |
| .MBN | Samsung Electronics | System Files | Multi Boot Image | Google Android | Google |
| .MBR | GNU Operating System | System Files | Master Boot Record File | GNU GRUB | GNU Operating System |
| .MDMP | Microsoft Corporation | System Files | Windows Minidump | Microsoft Visual Studio | Microsoft Corporation |
| .ME | Unknown Developer | System Files | Temporary Delete Me File | Unknown Software | Unknown Developer |
| .MEM | Microsoft Corporation | System Files | FoxPro Variable File | Microsoft Visual FoxPro | Microsoft Corporation |
| .METADATA_NEVER_INDEX | Apple | System Files | Spotlight Never Index File | macOS | Apple |
| .MFT | Kaspersky Lab | System Files | Kaspersky File Table | Kaspersky Anti-Virus | Kaspersky Lab |
| .MI4 | NVIDIA | System Files | Audio Player Firmware File | Rockbox Utility | Open Source |
| .MKEXT | Apple | System Files | Mac OS X Mach Kernel Extension Memory Cache | macOS | Apple |
| .MLB | Avanquest Software | System Files | MyLabel Designer Deluxe Project File | MyLabel Designer Deluxe | Avanquest Software |
| .MLC | Microsoft Corporation | System Files | Microsoft Language Interface Pack | Microsoft Windows | Microsoft Corporation |
| .MMV | Sony | System Files | MicroMV Video File | Squared 5 MPEG Streamclip | Open Source |
| .MOD | Open Source | System Files | Amiga Music Module File | ModPlug Player | Open Source |
| .MOT | NewTek | System Files | LightWave Motion File | LightWave 3D | NewTek |
| .MPA | Unknown Developer | System Files | MPEG-2 Audio File | Microsoft Windows Media Player | Microsoft Corporation |
| .MSC | Microsoft Corporation | System Files | Microsoft C Makefile | Microsoft Visual C++ | Microsoft Corporation |
| .MSP | Microsoft Corporation | System Files | Windows Installer Patch | Windows Installer | Microsoft Corporation |
| .MSSTYLES | Microsoft Corporation | System Files | Windows XP Style | Microsoft Windows | Microsoft Corporation |
| .MSU | Microsoft Corporation | System Files | Windows Vista Update Package | Microsoft Windows | Microsoft Corporation |
| .MUI | Myriad Software | System Files | Myriad User Instrument File | Myriad Harmony Assistant | Myriad Software |
| .MUM | AmsterCHEM | System Files | MATLAB Unit Operation Model File | AmsterCHEM MATLAB CAPE-OPEN Unit Operation | AmsterCHEM |
| .MYDOCS | Microsoft Corporation | System Files | Send To My Documents | Microsoft Windows | Microsoft Corporation |
| .NB0 | Unknown Developer | System Files | Device Boot Loader Image | Microsoft Windows CE Device Emulator | Microsoft Corporation |
| .NEI NASTRAN BULK DATA FILE | NEi Software | System Files | NEi Nastran Bulk Data File | NEi Nastran | NEi Software |
| .NFO | Microsoft Corporation | System Files | System Information File | Microsoft System Information | Microsoft Corporation |
| .NLD | ATI Technologies | System Files | ATI Radeon Video Driver File | Microsoft Windows | Microsoft Corporation |
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