| .ILG | Flexera Software | Arquivos de dados | InstallScript Log File | Unknown Software | Unknown Developer |
| .ILJ | Honest Technology | Arquivos de dados | Honestech VHS To DVD Project | honestech VHS to DVD | Honest Technology |
| .ILOGICVB | Autodesk, Inc. | Arquivos de dados | iLogic VB File | Autodesk Inventor | Autodesk, Inc. |
| .ILR | Unity Technologies | Arquivos de dados | Unity 3D License Request | Unity Technologies Unity | Unity Technologies |
| .ILV | IBM Cognos | Arquivos de dados | ILOG File | ILOG CPLEX Optimization Studio | IBM |
| .ILX | Andrew Quilley | Arquivos de dados | Interlex Vocabulary Data | Interlex | Andrew Quilley |
| .IMA | Sage | Arquivos de dados | Sage ACT! Email Message | Act! | Swiftpage, Inc. |
| .IMAGE | Apple | Arquivos de dados | Apple Disk Image | Roxio Toast 15 | Roxio |
| .IMB | Perion Network Ltd | Arquivos de dados | IncredMail Address Book And Temporary Contacts Data | IncrediMail | Perion Network Ltd |
| .IMD | Various Developers | Arquivos de dados | GIS Image Metadata File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .IMF | id Software | Arquivos de dados | Id Music File | CocoModX | Open Source |
| .IMH | Perion Network Ltd | Arquivos de dados | IncrediMail contacts Export File | IncrediMail | Perion Network Ltd |
| .IMK | Perion Network Ltd | Arquivos de dados | IncrediMail License | IncrediMail | Perion Network Ltd |
| .IMP | Lotus Software | Arquivos de dados | Improv Spreadsheet File | Lotus 1-2-3 | IBM |
| .IMR | IBM | Arquivos de dados | Impromptu Report File | IBM Cognos Impromptu | Symitar |
| .IMS | CursorArts Company | Arquivos de dados | IconForge Create Executable Library Data | IconForge | CursorArts Company |
| .IMT | Intuit, Inc. | Arquivos de dados | My Time Data File | macOS | Apple |
| .IN | Bitplane | Arquivos de dados | SmartGENERATOR Template File | smartGenerator | Bitplane |
| .IN3 | Harvard Graphics | Arquivos de dados | Harvard Graphics Input Device Driver File | Harvard Graphics ChartXL | Harvard Graphics |
| .IN4 | Phixsoft | Arquivos de dados | InfoBlaster IN4 Registry File | InfoBlaster IN4 | Phixsoft |
| .INA | Microsoft Corporation | Arquivos de dados | MS-DOS Data File | MS-DOS | Microsoft Corporation |
| .INDEX | The Eclipse Foundation | Arquivos de dados | Eclipse Help Index | Eclipse CDT | The Eclipse Foundation |
| .INI | Microsoft Corporation | Arquivos de dados | Windows Initialization File | Notepad++ | Don Ho |
| .INK | Mimio | Arquivos de dados | Mimio Ink Data File | MimioStudio | Mimio |
| .INP | Concept Software | Arquivos de dados | Urdu InPage Document | Urdu InPage | Concept Software |
| .INS | Open Source | Arquivos de dados | LaTeX Installer Script | Microsoft Notepad | Microsoft Corporation |
| .INSID | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .INST | Interscape | Arquivos de dados | RMCProfile Peak Profile Data | RMCProfile | Interscape |
| .INSTALLER | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .INSTALLLOG | Microsoft Corporation | Arquivos de dados | Microsoft .NET Installation Log | Microsoft Visual Studio | Microsoft Corporation |
| .INSTR | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .INTEGER | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .INTRO | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .INV | Copyboy | Arquivos de dados | INVedit File | INVedit | Copyboy |
| .INVENTOR | Open Source | Arquivos de dados | SGI Open Inventor File | Open Inventor | Open Source |
| .IP | Stardock Corporation | Arquivos de dados | Icon Packager Theme File | Stardock Icon Packager | Stardock Corporation |
| .IPJ | Autodesk, Inc. | Arquivos de dados | Inventor Project File | Autodesk Inventor | Autodesk, Inc. |
| .IPR | Flexera Software | Arquivos de dados | InstallShield Project | InstallShield | Flexera Software |
| .IQC | International TechneGroup Incorporated | Arquivos de dados | CADIQ Comparison Analysis Result | CADIQ | International TechneGroup Incorporated |
| .IQF | IRIS | Arquivos de dados | Integra Query File | Integra | IRIS |
| .IQR | International TechneGroup Incorporated | Arquivos de dados | CADIQ View Analysis Results | CADIQ | International TechneGroup Incorporated |
| .IQS | International TechneGroup Incorporated | Arquivos de dados | CADIQ Summary File | CADIQ | International TechneGroup Incorporated |
| .IR | Crestron Electronics | Arquivos de dados | DEAL For Windows File | DEAL | Crestron Electronics |
| .IRI | GRAYESS | Arquivos de dados | Infrared Image | IRT Cronista | GRAYESS |
| .IROCK | Engius | Arquivos de dados | IntelliRock Sensor Data File | Engius rockWare | Engius |
| .IRP | Zylox Software, Inc. | Arquivos de dados | Internet Researcher Project File | Internet Researcher | Zylox Software, Inc. |
| .IRX | Martin Stanek | Arquivos de dados | Brewer Irradiation File | UVBrewer | Interscape |
| .IS2 | GRAYESS | Arquivos de dados | Thermal Image Data File | IRT Cronista | GRAYESS |
| .ISC | Xilinx, Inc. | Arquivos de dados | Xilinx Device Configuration File | Xilinx Platform Studio (XPS) | Xilinx, Inc. |
| .ISD | Flexera Software | Arquivos de dados | Flexera InstallShield Dialog Box File | InstallShield | Flexera Software |
| .ISF | Inspiration Software Inc. | Arquivos de dados | Inspiration Flowchart Document | Inspiration Software | Inspiration Software Inc. |
| .IST | Flexera Software | Arquivos de dados | InstallShield Project Template File | InstallShield | Flexera Software |
| .ISV | Harris Geospatial Solutions | Arquivos de dados | IDL iTools State | IDL | Harris Geospatial Solutions |
| .IT3 | Unknown Developer | Arquivos de dados | Internet Timer 3 Log | Unknown Software | Unknown Developer |
| .ITD | SDL Trados | Arquivos de dados | SDL Trados Translation File | SDL Trados | SDL Trados |
| .ITE | Apple | Arquivos de dados | iTunes Extras File | Apple iTunes | Apple |
| .ITF | Interactive Data Corporation | Arquivos de dados | eSignal Integrated Trading Data | eSignal | Interactive Data Corporation |
| .ITL | Apple | Arquivos de dados | iTunes Library File | Apple iTunes | Apple |
| .ITM | isee systems | Arquivos de dados | iThink Model File | iThink Architect | isee systems |
| .ITN | TomTom International BV | Arquivos de dados | TomTom Navigator Itinerary File | TomTom HOME | TomTom NV |
| .ITP | BioWare | Arquivos de dados | Bioware Palette Data | BioWare Neverwinter Nights | BioWare |
| .ITRACE | Microsoft Corporation | Arquivos de dados | Microsoft Visual Studio Data File | Microsoft Visual Studio | Microsoft Corporation |
| .ITU | Unknown Developer | Arquivos de dados | Shefield Dictionary | Unknown Software | Unknown Developer |
| .ITW | Prairie Group | Arquivos de dados | InTouch With Database File | Prairie Group InTouch With | Prairie Group |
| .ITX | IBM | Arquivos de dados | ITX Form Template | FileNet eForms | IBM |
| .IUT | Open Source | Arquivos de dados | SPaCIoS Tool IUT Definition | SPaCIoS Tool | Open Source |
| .IVC | InteliSea | Arquivos de dados | InteliSea Vessel Configuration File | InteliSea Configuration Manager | InteliSea |
| .IVD | Bitdefender | Arquivos de dados | Incremental Virus Definitions File | Bitdefender Total Security 2018 | Bitdefender |
| .IVI | Microsoft Corporation | Arquivos de dados | MSDN InfoViewer Topic Data | Microsoft Visual Studio | Microsoft Corporation |
| .IVN | Microsoft Corporation | Arquivos de dados | iView MediaPro Catalogue File | iView Media Pro | iView Multimedia |
| .IVP | Oracle Corporation | Arquivos de dados | Panorama File | Java | Oracle Corporation |
| .IVS | Thomas d'Otreppe de Bouvette | Arquivos de dados | Initialization Vector File | Aircrack-ng | Thomas d'Otreppe de Bouvette |
| .IVT | AddGames Italia | Arquivos de dados | International Volleyball 2006 Data File | International Volleyball 2006 | AddGames Italia |
| .IW | IWIS | Arquivos de dados | Chain Engineering Database File | Chain Engineering | IWIS |
| .IWL | Incomedia | Arquivos de dados | WebSite X5 License File | Website X5 | Incomedia |
| .IWM | iWriteMusicProject | Arquivos de dados | iWriteMusic Song Exchange Format | iWriteMusic | iWriteMusicProject |
| .IX | Corel | Arquivos de dados | Corel WordPerfect Office Template File | Corel WordPerfect | Corel |
| .IXB | Corel | Arquivos de dados | Ulead Disc Image | DVD MovieFactory | Corel |
| .IXC | ESRI (Environmental Systems Research Institute) | Arquivos de dados | ArcView Geocoding Index For Read-Write Coverages File | ESRI ArcGIS for Desktop | ESRI (Environmental Systems Research Institute) |
| .IXE | Unknown Developer | Arquivos de dados | InterEX Control File | Unknown Software | Unknown Developer |
| .IXF | IBM | Arquivos de dados | Integration Exchange Format File | IBM DB2 | IBM |
| .IXR | System Simulation | Arquivos de dados | Index+ For Windows Report Definition File | Index+ | System Simulation |
| .IZD | United Planet | Arquivos de dados | Intrexx Application Export Format | Intrexx | United Planet |
| .J1 | Unknown Developer | Arquivos de dados | EDIT Compiler JEDEC Boundary File | Unknown Software | Unknown Developer |
| .JASPER | Jaspersoft | Arquivos de dados | JasperReports Data File | JasperReports | Jaspersoft |
| .JAW | JustSystems | Arquivos de dados | Ichitaro File | Ichitaro | JustSystems |
| .JBB | Damian Brunold | Arquivos de dados | Jbead Data | Jbead | Damian Brunold |
| .JBD | Symantec Corporation | Arquivos de dados | Norton Antivirus Definiton Update File Format | Norton Security | Symantec Corporation |
| .JBI | Yaskawa Motoman | Arquivos de dados | Motoman Robot Job File | MotoPallet EG | Yaskawa Motoman |
| .JBW | Scitor | Arquivos de dados | Scitor Project Scheduler Schedule Data | Project Scheduler | Scitor |
| .JBX | Unknown Developer | Arquivos de dados | Project Scheduler Data | Unknown Software | Unknown Developer |
| .JCAMP | Joint Committee on Atomic and Molecular Physical Data (JCAMP-DX ) | Arquivos de dados | JCAMP Standard NMR Data Format | Unknown Software | Unknown Developer |
| .JCC | Open Source | Arquivos de dados | Code Crusader Project Data | Code Crusader | Open Source |
| .JCD | Hou Yantang | Arquivos de dados | FlashGet Saved Data | FlashGet | Hou Yantang |
| .JCE | Glenn Rosenthal | Arquivos de dados | JWPce File | JWPce | Glenn Rosenthal |
| .JCK | Microsoft Corporation | Arquivos de dados | Microsoft Liquid Motion JACK Scene Escription | Liquid Motion | Microsoft Corporation |
| .JCV | JC Video | Arquivos de dados | JC Video Systems Data | Unknown Software | Unknown Developer |
| .JD | Orchid Technology KK | Arquivos de dados | Jigsaw Terminal File | Jigsaw Platform | Orchid Technology KK |
| .JDB | Symantec Corporation | Arquivos de dados | Symantec Endpoint Protection Update File | Symantec EndPoint Protection 12 | Symantec Corporation |
| .JDBG | Open Source | Arquivos de dados | Embedded JCL Debug Information | Project JEDI | Open Source |
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