| .HTMLZ | Open Source | Arquivos eBook | Zipped HTML Document Or E-book | Calibre | Open Source |
| .HTS | Open Source | Arquivos de configuração | HyperTuner Skin | HyperTuner | Open Source |
| .HTX | Microsoft Corporation | Arquivos Web | HTML Extension File | Notepad2 | Open Source |
| .HVC | Sublime HQ Pty Ltd | Arquivos de Texto | ASCII Text | Notepad2 | Open Source |
| .HWD | Hedgewars Project | Arquivos de jogos | Hedgewars Demo File | Hedgewars | Open Source |
| .HWL | Corel | Arquivos de dados | Corel Writing Tools File | Hangman Deluxe | Open Source |
| .HWMAP | Hedgewars Project | Arquivos de jogos | Hedgewars Drawn Map File | Hedgewars | Open Source |
| .HWS | Hedgewars Project | Arquivos de jogos | Hedgewars Saved Game | Hedgewars | Open Source |
| .HWV | Open Source | Arquivos de dados | Hades Waveform Viewer Data | Hades simulation framework | Open Source |
| .HX | Thermo Fisher Scientific Inc. | Arquivos 3D | Amira 3D Mesh File | Haxe | Open Source |
| .HXML | Open Source | Arquivos de desenvolvedor | HaXe Make File | Haxe | Open Source |
| .I | Microsoft Corporation | Arquivos de desenvolvedor | Visual Studio Intermediate File | INTERCAL | Open Source |
| .I00 | Daemon Tools | Arquivos de imagem de disco | DVD Shrink Part 1 File | DVDShrink | Open Source |
| .I02 | Disc Soft Ltd. | Arquivos de imagem de disco | DVD Shrink Part 3 File | DVDShrink | Open Source |
| .IBL | Open Source | Arquivos de dados | sIBL System Data | sIBL-Edit | Open Source |
| .ICAL | Open Source | Arquivos miscelâneas | iCalendar File | PHP iCalendar | Open Source |
| .ICALENDAR | Open Source | Arquivos miscelâneas | iCalendar File | PHP iCalendar | Open Source |
| .ICE | Raphaël et Béatrice Mounier | Arquivos comprimidos | ICE File Archive | IceChat IRC | Open Source |
| .ICF | Zoom Telephonics | Arquivos de cópia | Zoom Router Configuration File | AbiWord | Open Source |
| .ICO | The GIMP Development Team | Arquivos de sistema | Icon File | IrfanView | Open Source |
| .IDX | Unknown Developer | Arquivos miscelâneas | Movie Subtitle File | SMPlayer | Open Source |
| .IFF | Electronic Arts | Arquivos de áudio | Interchange File Format | IrfanView | Open Source |
| .IFILE | Open Source | Arquivos Web | Amaya I386 File | Amaya | Open Source |
| .IG | elego Software Solutions GmbH | Arquivos miscelâneas | Modula-3 Generic Interface Source | iSpy | Open Source |
| .IGC | Open Source | Arquivos de dados | Anime List Builder Input File | Anime List Builder | Open Source |
| .IGP | Open Source | Arquivos de áudio | Igor Published Music Notation File | NoteHeads Igor Reader | Open Source |
| .IGS | United States Air Force | Arquivos CAD | Initial Graphics Exchange Specification Drawing File | FreeCAD | Open Source |
| .IJS | Open Source | Arquivos de desenvolvedor | J Interpretor Script | J language | Open Source |
| .IJX | Jsoftware | Arquivos de desenvolvedor | J Language Execution Window | J language | Open Source |
| .IKM | Open Source | Arquivos de dados | XWE Data | XWE | Open Source |
| .ILBM | Electronic Arts | Arquivos de imagem Raster | Interleaved Bitmap Image | IrfanView | Open Source |
| .ILD | Open Source | Arquivos de dados | XWE Data | XWE | Open Source |
| .ILF | Open Source | Arquivos de dados | Alim File | Alim | Open Source |
| .IM1 | Sun Microsystems | Arquivos de imagem Raster | Sun Raster Image File | IrfanView | Open Source |
| .IM8 | Sun Microsystems | Arquivos de imagem Raster | Sun Raster Graphic File | IrfanView | Open Source |
| .IMAGE | Apple | Arquivos de imagem de disco | Apple Disk Image | OpenQwaq | Open Source |
| .IMF | id Software | Arquivos de áudio | Id Music File | CocoModX | Open Source |
| .IMG | Unknown Developer | Arquivos de imagem de disco | Disk Image Data File | IrfanView | Open Source |
| .IML | JetBrains | Arquivos de desenvolvedor | IntelliJ IDEA Module | Notepad2 | Open Source |
| .IN | Bitplane | Arquivos de dados | SmartGENERATOR Template File | Notepad2 | Open Source |
| .INB | LucasArts Entertainment Company, LLC | Arquivos de jogos | Rebel Assault Backup | Embroidermodder 2 | Open Source |
| .INFO | GNU Project | Arquivos miscelâneas | Texinfo Document | Minecraft Forge | Open Source |
| .INI | Microsoft Corporation | Arquivos de configuração | Windows Initialization File | PSPad | Open Source |
| .INO | Jordan Russell | Arquivos de configuração | Inno Setup Script | Inno Setup | Open Source |
| .INP | Concept Software | Arquivos de layout de página | Urdu InPage Document | gretl | Open Source |
| .INS | Open Source | Arquivos de dados | LaTeX Installer Script | Notepad2 | Open Source |
| .INV | Copyboy | Arquivos de jogos | INVedit File | MCEdit | Open Source |
| .INVENTOR | Open Source | Arquivos de dados | SGI Open Inventor File | Open Inventor | Open Source |
| .IO | Open Source | Arquivos comprimidos | CPIO Compressed File Archive | Linux | Open Source |
| .IPK | Open Source | Arquivos comprimidos | Itsy Package | Debian software (dpkg) | Open Source |
| .IPOD | Open Source | Arquivos de sistema | Rockbox Firmware File | Rockbox Utility | Open Source |
| .IPS | ZeroSoft Zophar | Arquivos de jogos | Internal Patching System Patch File | MultiPatch patching tool | Open Source |
| .IRZ | Open Source | Arquivos comprimidos | iROS Application Packaging Unit | iROS | Open Source |
| .ISO | Igor Pavlov | Arquivos de imagem de disco | Disc Image File | PCSX2 | Open Source |
| .ISR | Open Source | Arquivos de jogos | GoMoku Game File | Gomoku | Open Source |
| .ISS | Jordan Russell | Arquivos de configuração | Inno Setup Script | Inno Setup | Open Source |
| .IT | Open Source | Arquivos de áudio | Impulse Tracker Module | ModPlug Player | Open Source |
| .ITHMB | Apple | Arquivos de imagem Raster | iPod And iPhone Photo Thumbnails File | Keith's iPod Photo Reader | Open Source |
| .ITI | Open Source | Arquivos de áudio | Impulse Tracker Instrument | CocoModX | Open Source |
| .ITS | Open Source | Arquivos de áudio | Impulse Tracker Sample | CocoModX | Open Source |
| .ITZ | Microsoft Corporation | Arquivos de áudio | Impulse Tracker Music Module | Impulse Tracker | Open Source |
| .IUT | Open Source | Arquivos de dados | SPaCIoS Tool IUT Definition | SPaCIoS Tool | Open Source |
| .IVE | Open Source | Arquivos 3D | OpenSceneGraph Binary File | OpenSceneGraph | Open Source |
| .J | Oracle Corporation | Arquivos de desenvolvedor | Java Source File | gVim | Open Source |
| .J01 | Open Source | Arquivos de cópia | Akeeba Multi-part Backup Archive | Akeeba eXtract Wizard | Open Source |
| .J2K | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG 2000 Image | IrfanView | Open Source |
| .JAS | Open Source | Arquivos 3D | Cheetah3D Model File | Cheetah3D | Open Source |
| .JAV | Oracle Corporation | Arquivos de desenvolvedor | Java Source Code | gVim | Open Source |
| .JAVA | Oracle Corporation | Arquivos de desenvolvedor | Java Source Code | gVim | Open Source |
| .JBP | Open Source | Arquivos miscelâneas | Jabaco Project | Jabaco | Open Source |
| .JCC | Open Source | Arquivos de dados | Code Crusader Project Data | Code Crusader | Open Source |
| .JDBG | Open Source | Arquivos de dados | Embedded JCL Debug Information | Project JEDI | Open Source |
| .JGC | Open Source | Arquivos miscelâneas | JGCGen Script | JGCGen | Open Source |
| .JIF | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG Image | IrfanView | Open Source |
| .JKS | Oracle Corporation | Arquivos codificados | Java Keystore File | KeyStore Explorer | Open Source |
| .JL | Julian Gabriel Casadesus and Others | Arquivos de desenvolvedor | Julia Source Code File | Julia | Open Source |
| .JOBS | Open Source | Arquivos de configuração | VirtualDub Job File | VirtualDub | Open Source |
| .JOINED | Freebyte | Arquivos de dados | HJ-Split Data File | HJ-Split | Open Source |
| .JP4 | Open Source | Arquivos comprimidos | Elphel Project Data | Elphel Project | Open Source |
| .JPA | Open Source | Arquivos de cópia | Akeeba Backup Archive | Akeeba eXtract Wizard | Open Source |
| .JPEG | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG Image | IrfanView | Open Source |
| .JPF | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG 2000 Image | IrfanView | Open Source |
| .JPG | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG Image | IrfanView | Open Source |
| .JPG-LARGE | Zoner Software | Arquivos de imagem Raster | Large JPEG Image | IrfanView | Open Source |
| .JPG2 | Joint Photographic Experts Group | Arquivos de imagem Raster | JPEG 2000 Image | IrfanView | Open Source |
| .JPM | Irfan Skiljan | Arquivos Gráficos | JPEG 2000 Multi-layer Image Format (ISO 15444-6) | IrfanView | Open Source |
| .JPQ | Open Source | Arquivos comprimidos | JPQ (Jared Package) Library Archive | JPQ (Jared Package) Library | Open Source |
| .JPS | Open Source | Arquivos de cópia | Akeeba Backup Archive | Akeeba eXtract Wizard | Open Source |
| .JPX | Embarcadero Technologies | Arquivos de desenvolvedor | JBuilder Project | IrfanView | Open Source |
| .JRC | Open Source | Arquivos de jogos | PCjr Cartridge ROM File | DOSBox | Open Source |
| .JS | NetScape | Arquivos Web | JavaScript File | JACOsub | Open Source |
| .JSE | Microsoft Corporation | Arquivos executáveis | JScript Encoded File | Notepad2 | Open Source |
| .JSF | Adobe Systems Incorporated | Arquivos Web | Java Script Command File | Project64 | Open Source |
| .JSH | Freedom Scientific | Arquivos de desenvolvedor | JAWS Script Header File | Jsh | Open Source |
| .JSON | Mozilla | Arquivos de cópia | Mozilla Firefox Bookmarks Backup | Pico | Open Source |
| .JSPA | Xinox Software | Arquivos Web | Java Servlet Alias | Amaya | Open Source |
| .JST | Jabosoft | Arquivos de jogos | Jnes Save State | Code Crusader | Open Source |
| .JWW | Open Source | Arquivos de dados | Java Web-Workflows Data | Java Web-Workflows | Open Source |
| .KAN | Open Source | Arquivos de dados | Kwalitan Annotation | Kwalitan | Open Source |
| .KBD | Autodesk, Inc. | Arquivos de configuração | 3ds Max Keyboard Shortcuts File | Janko's Keyboard Generator | Open Source |
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