| .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 |
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