| .I3A | Zepetto | Fichiers de jeu | Point Blank Game Data File | I3Play | Ini3 Digital PLC |
| .I3ANIMPACK | Zepetto | Fichiers de jeu | Point Blank Game Data File | I3Play | Ini3 Digital PLC |
| .I3CHR | Zepetto | Fichiers de jeu | Point Blank Game Audio Data | Point Blank | Zepetto |
| .I3EXEC | Zepetto | Fichiers de jeu | Point Blank Game Data File | I3Play | Ini3 Digital PLC |
| .I3PACK | Zepetto | Fichiers de jeu | Point Blank Game Data File | I3Play | Ini3 Digital PLC |
| .I3S | Zepetto | Fichiers de jeu | Point Blank Game Data File | I3Play | Ini3 Digital PLC |
| .IAO | Imperium Games | Fichiers de jeu | ImperiumAO Game Data | ImperiumAO | Imperium Games |
| .IBF | Square Enix | Fichiers de jeu | Final Fantasy XI Game Data | Final Fantasy XI | Square Enix |
| .IBT | Eidos Interactive | Fichiers de jeu | Texture And Model File | Deadly Shadows | Eidos Interactive |
| .ICD | Macrovision Corporation | Fichiers de jeu | SafeDisc Encrypted Program | SafeDisc | Macrovision Corporation |
| .ID | IBM | Fichiers de jeu | Lotus Notes User ID File | IBM Lotus Notes | IBM |
| .IDE | Rockstar Games | Fichiers de jeu | GTA Item Definition File | Grand Theft Auto IV | Rockstar Games |
| .IDM | Ulead Systems | Fichiers de jeu | Ulead Photo Express Messages File | Ulead Photo Express | Ulead Systems |
| .IDS | BioWare | Fichiers de jeu | BioWare Infinity Game Engine Data | Baldur's Gate | BioWare |
| .IFL | Autodesk, Inc. | Fichiers de jeu | 3ds Max Image File List | Autodesk 3ds Max | Autodesk, Inc. |
| .IFP | Rockstar Games | Fichiers de jeu | GTA Animation File | Grand Theft Auto IV | Rockstar Games |
| .IFR | Sony | Fichiers de jeu | Formula One 2001 Game File | Formula One 2001 | Psygnosis |
| .IKL | Microsoft Corporation | Fichiers de jeu | InkBall Game Data | InkBall | Microsoft Corporation |
| .IM | Sun Microsystems | Fichiers de jeu | SunOS Grey Scale Bitmap Picture | SunOS | Sun Microsystems |
| .IMC | LucasArts Entertainment Company, LLC | Fichiers de jeu | LucasArts Game Sound | X-Wing Alliance | LucasArts Entertainment Company, LLC |
| .IMG | Unknown Developer | Fichiers de jeu | Disk Image Data File | IsoBuster | Smart Projects |
| .IMS | CursorArts Company | Fichiers de jeu | IconForge Create Executable Library Data | IconForge | CursorArts Company |
| .IMU | LucasArts Entertainment Company, LLC | Fichiers de jeu | Star Wars Force Commander Audio File | Star Wars: Force Commander | LucasArts Entertainment Company, LLC |
| .INB | LucasArts Entertainment Company, LLC | Fichiers de jeu | Rebel Assault Backup | Star Wars: Rebel Assault | LucasArts Entertainment Company, LLC |
| .INDEX | The Eclipse Foundation | Fichiers de jeu | Eclipse Help Index | Eclipse CDT | The Eclipse Foundation |
| .INFO | GNU Project | Fichiers de jeu | Texinfo Document | GNU Emacs | GNU Project |
| .INN | Micro Focus International plc | Fichiers de jeu | Micro Focus COBOL/2 Overlay File | IBM COBOL | IBM |
| .INP | Concept Software | Fichiers de jeu | Urdu InPage Document | Urdu InPage | Concept Software |
| .INV | Copyboy | Fichiers de jeu | INVedit File | INVedit | Copyboy |
| .IO | Open Source | Fichiers de jeu | CPIO Compressed File Archive | Linux | Open Source |
| .IOP | Z8Games | Fichiers de jeu | Lost Saga Game Data | Lost Saga | I.O. Entertainment |
| .IPL | Rockstar Games | Fichiers de jeu | GTA Item Placement File | Grand Theft Auto III | Rockstar Games |
| .IPS | ZeroSoft Zophar | Fichiers de jeu | Internal Patching System Patch File | MultiPatch patching tool | Open Source |
| .ISB | Sony | Fichiers de jeu | Vanguard Music File | Vanguard: Saga of Heroes | Sony |
| .ISD | Flexera Software | Fichiers de jeu | Flexera InstallShield Dialog Box File | InstallShield | Flexera Software |
| .ISR | Open Source | Fichiers de jeu | GoMoku Game File | Gomoku | Open Source |
| .ITM | isee systems | Fichiers de jeu | iThink Model File | iThink Architect | isee systems |
| .ITP | BioWare | Fichiers de jeu | Bioware Palette Data | BioWare Neverwinter Nights | BioWare |
| .ITR | Free Lunch Design | Fichiers de jeu | File TypeIcy Tower Replay File | Icy Tower | Free Lunch Design |
| .IVT | AddGames Italia | Fichiers de jeu | International Volleyball 2006 Data File | International Volleyball 2006 | AddGames Italia |
| .IWD | Activision | Fichiers de jeu | Call Of Duty Game Data File | Corel WinZip 21 | Corel |
| .IX3 | Lokasoft | Fichiers de jeu | Rebel Chess Program File | Rebel | Lokasoft |
| .IX4 | Lokasoft | Fichiers de jeu | Rebel Chess File | Rebel | Lokasoft |
| .J2B | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 Music Data | Jazz Jackrabbit 2 | Epic Games |
| .J2D | Epic Games | Fichiers de jeu | Jazz Jackrabbit Data File | Jazz Jackrabbit | Epic Games |
| .J2E | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 Episode File | Jazz Jackrabbit 2 | Epic Games |
| .J2H | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 High Scores | Jazz Jackrabbit 2 | Epic Games |
| .J2I | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 Internet Server Link File | Jazz Jackrabbit 2 | Epic Games |
| .J2L | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 Level File | Jazz Jackrabbit 2 | Epic Games |
| .J2T | Epic Games | Fichiers de jeu | Jazz Jackrabbit 2 Tile Set | Jazz Jackrabbit 2 | Epic Games |
| .JA | Trainz portal | Fichiers de jeu | Jet Archive | N3V Games Trainz Simulator | Trainz portal |
| .JAG | Jagex | Fichiers de jeu | Jagex Data File | RuneScape | Jagex |
| .JAM | Sierra Entertainment | Fichiers de jeu | Leisure Suit Larry Magna Cum Laude Archive File | Leisure Suit Larry: Magna Cum Laude | Sierra Entertainment |
| .JAP | Alexander S. Meshcheryakov | Fichiers de jeu | Nonogram Puzzle File | QNonograms | Alexander S. Meshcheryakov |
| .JBL | id Software | Fichiers de jeu | Doom Scene Add-on File | Doom | id Software |
| .JDF | Adobe Systems Incorporated | Fichiers de jeu | Adobe Acrobat Job Definition File | Adobe Acrobat DC | Adobe Systems Incorporated |
| .JG6 | Lena Games | Fichiers de jeu | BigJig Jigsaw Data | BigJig | Lena Games |
| .JIG | GameHouse | Fichiers de jeu | GameHouse Puzzle Jigsaw Game Data | Jigsaw World | Inertia Software |
| .JIGSAW | Carolina Road Software L.L.C. | Fichiers de jeu | Jigsaw Explorer Puzzle | Jigsaw Explorer | Carolina Road Software L.L.C. |
| .JKL | LucasArts Entertainment Company, LLC | Fichiers de jeu | Jedi Knight File | Star Wars Jedi Knight: Dark Forces II | LucasArts Entertainment Company, LLC |
| .JKS | Oracle Corporation | Fichiers de jeu | Java Keystore File | Unity Technologies Unity | Unity Technologies |
| .JMF | Chain Studios | Fichiers de jeu | Jackhammer Project | J.A.C.K | Chain Studios |
| .JN1 | Epic Games | Fichiers de jeu | Jill Of The Jungle Data File | Jill Of The Jungle | Epic Games |
| .JNC | Hypnos Entertainment | Fichiers de jeu | Jack Nicklaus 6 Course Data | Jack Nicklaus 6: Golden Bear Challenge | Hypnos Entertainment |
| .JNK | Little Green Men Games | Fichiers de jeu | Starpoint Gemini 2 Junkyard Data | Starpoint Gemini 2 | Little Green Men Games |
| .JPK | JPK Instruments | Fichiers de jeu | JPK Instruments File Format | Unknown Software | Unknown Developer |
| .JPN | Microsoft Corporation | Fichiers de jeu | Windows Japanese Noise-Word List File | Microsoft Notepad | Microsoft Corporation |
| .JPP | Bitz & Pixelz | Fichiers de jeu | Jigsaw Puzzle Player Puzzle Definition | Jigsaw Puzzle Player | Bitz & Pixelz |
| .JPZ | WordWeb Software | Fichiers de jeu | Puzzle Solver Puzzle File | Crossword Solver | WordWeb Software |
| .JRC | Open Source | Fichiers de jeu | PCjr Cartridge ROM File | DOSBox | Open Source |
| .JRF | Unknown Developer | Fichiers de jeu | The Jumbot Bot Level Navigation Data | Half-Life | Valve |
| .JRL | BioWare | Fichiers de jeu | BioWare Aurora Game Engine Journal Data | BioWare Neverwinter Nights | BioWare |
| .JST | Jabosoft | Fichiers de jeu | Jnes Save State | Jnes | Jabosoft |
| .K2S | Mantronic Software | Fichiers de jeu | Kaiser 2 Saved Game | Kaiser 2 | Mantronic Software |
| .KA | Epic Games | Fichiers de jeu | Karma Engine Asset Data | Unreal Tournament | Epic Games |
| .KCH | Ark Angles | Fichiers de jeu | KChess Game File | KChess | Ark Angles |
| .KCL | Nintendo | Fichiers de jeu | Mario Kart Collision File | Mario Kart Wii | Nintendo |
| .KEY | Unknown Developer | Fichiers de jeu | License/ Encrypted Security Key File | Avira Antivirus Pro 2016 | Avira Operations GmbH & Co. KG. |
| .KF2 | Rockstar Games | Fichiers de jeu | Max Payne Resource File | chUmbaLum sOft MilkShape 3D | chUmbaLum sOft |
| .KFN | Recisio | Fichiers de jeu | KaraFun Karaoke File | KaraFun | Recisio |
| .KFS | Rockstar Games | Fichiers de jeu | Max Payne Model File | chUmbaLum sOft MilkShape 3D | chUmbaLum sOft |
| .KMP | Korg | Fichiers de jeu | Korg Trinity/Triton Keymap File | Awave Studio | FMJ-Software |
| .KN5 | Kunos Simulazioni | Fichiers de jeu | Assetto Corsa 3D Object | Assetto Corsa | Kunos Simulazioni |
| .KOR | Epic Games | Fichiers de jeu | Unreal Engine Language Localization | Unreal Tournament | Epic Games |
| .KPR | Open Source | Fichiers de jeu | KPresenter Presentation | KOffice | Open Source |
| .KRN | EA Maxis | Fichiers de jeu | NBA Live 99 Fonts File | NBA Live 99 | Electronic Arts |
| .KSV | Kheops Studio Company | Fichiers de jeu | Kheops Studio Video | Kheops Studio | Kheops Studio Company |
| .KTO | Kunos Simulazioni | Fichiers de jeu | NetKar Pro Mid Ohio Data | netKar Pro | Kunos Simulazioni |
| .KVQ | Sega | Fichiers de jeu | Sega Smash Pack PC Version File | Sega Smash Pack | Sega |
| .KWD | KDE | Fichiers de jeu | KWord Document | KOffice | Open Source |
| .KYE | Colin Garbutt | Fichiers de jeu | Kye Level Data | Kye | Colin Garbutt |
| .L2R | NCSoft | Fichiers de jeu | Lineage II Replay File | NCSOFT Lineage II | Interscape |
| .LA1 | LucasArts Entertainment Company, LLC | Fichiers de jeu | LucasArts Game Data File | The Curse of Monkey Island | LucasArts Entertainment Company, LLC |
| .LAN | ESRI (Environmental Systems Research Institute) | Fichiers de jeu | ERDAS LAN File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .LANG | Mojang | Fichiers de jeu | Minecraft Language File | Microsoft Notepad | Microsoft Corporation |
| .LBA | ShopTalk Systems | Fichiers de jeu | Liberty BASIC Source Code | Liberty Basic | ShopTalk Systems |
| .LBI | Adobe Systems Incorporated | Fichiers de jeu | Dreamweaver Library Item | Adobe Dreamweaver | Adobe Systems Incorporated |
| .LBM | Electronic Arts | Fichiers de jeu | Deluxe Paint Bitmap Image File | Canvas X | ACD Systems |
| .LBW | CCP Games | Fichiers de jeu | CCP Log Server Utility Log File | EVE Online | CCP Games |
| .LCO | PopTop Software Inc. | Fichiers de jeu | Railroad Tycoon 3 Locomotive Properties | Railroad Tycoon 3 | PopTop Software Inc. |
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