| .I | Microsoft Corporation | Arquivos de desenvolvedor | Visual Studio Intermediate File | Microsoft Visual Studio | Microsoft Corporation |
| .I3 | elego Software Solutions GmbH | Arquivos de desenvolvedor | Modula-3 Interface Source Code | Modula-3 | elego Software Solutions GmbH |
| .IAP | BioWare | Arquivos de desenvolvedor | Infinity Engine Add-on Patcher File | Baldur's Gate | BioWare |
| .ICE | Raphaël et Béatrice Mounier | Arquivos de desenvolvedor | ICE File Archive | ALZip | ESTsoft |
| .IDAPI | Borland | Arquivos de desenvolvedor | Borland Database Engine IDAPI Data | Borland C++ | Micro Focus International plc |
| .IDB | Microsoft Corporation | Arquivos de desenvolvedor | Visual Studio Intermediate Debug File | Microsoft Visual Studio | Microsoft Corporation |
| .IDL | Microsoft Corporation | Arquivos de desenvolvedor | Interface Definition Language File | Microsoft Visual Studio | Microsoft Corporation |
| .IDT | Microsoft Corporation | Arquivos de desenvolvedor | Windows Installer Database Text Archive File | Windows Installer | Microsoft Corporation |
| .IHT | Unknown Developer | Arquivos de desenvolvedor | Intranet Connector Script File | Unknown Software | Unknown Developer |
| .II | Axialis Company | Arquivos de desenvolvedor | IconWorkshop Extended Information File | Axialis IconWorkshop | Axialis Company |
| .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 |
| .IK | Ola Bini | Arquivos de desenvolvedor | Ioke Script | Ioke | Ola Bini |
| .ILE | Cadence Design Systems | Arquivos de desenvolvedor | Encrypted Cadence SKILL File | SKILL | Cadence Design Systems |
| .ILK | Microsoft Corporation | Arquivos de desenvolvedor | Microsoft Visual Studio Linker Input File | Microsoft Visual Studio | Microsoft Corporation |
| .IMI | Embarcadero Technologies | Arquivos de desenvolvedor | Turbo Pascal DOS File | Turbo Pascal | Embarcadero Technologies |
| .IML | JetBrains | Arquivos de desenvolvedor | IntelliJ IDEA Module | Microsoft Notepad | Microsoft Corporation |
| .IMP | Lotus Software | Arquivos de desenvolvedor | Improv Spreadsheet File | Lotus 1-2-3 | IBM |
| .INC | Microsoft Corporation | Arquivos de desenvolvedor | Include File | MacroMates TextMate | MacroMates |
| .INH | Microsoft Corporation | Arquivos de desenvolvedor | Visual Basic Basfwin File | Microsoft Visual Basic | Microsoft Corporation |
| .INL | Microsoft Corporation | Arquivos de desenvolvedor | C++ Inline File | C++ | Bjarne Stroustrup |
| .INO | Jordan Russell | Arquivos de desenvolvedor | Inno Setup Script | Microsoft Notepad | Microsoft Corporation |
| .IPP | The Eclipse Foundation | Arquivos de desenvolvedor | Inline Guard Macro File | Microsoft Visual Studio | Microsoft Corporation |
| .IPR | Flexera Software | Arquivos de desenvolvedor | InstallShield Project | InstallShield | Flexera Software |
| .IPS | ZeroSoft Zophar | Arquivos de desenvolvedor | Internal Patching System Patch File | MultiPatch patching tool | Open Source |
| .IQT | Tektronix | Arquivos de desenvolvedor | Tektronix File | The MathWorks MATLAB | MathWorks |
| .IS | elego Software Solutions GmbH | Arquivos de desenvolvedor | Intermediate Assembly File | Modula-3 | elego Software Solutions GmbH |
| .ISA | Adobe Systems Incorporated | Arquivos de desenvolvedor | Adobe Photoshop ImageReady Action Data | Adobe Photoshop | Adobe Systems Incorporated |
| .ISC | Xilinx, Inc. | Arquivos de desenvolvedor | Xilinx Device Configuration File | Xilinx Platform Studio (XPS) | Xilinx, Inc. |
| .ISM | Microsoft Corporation | Arquivos de desenvolvedor | IIS Smooth Streaming Manifest File | Microsoft IIS | Microsoft Corporation |
| .IST | Flexera Software | Arquivos de desenvolvedor | InstallShield Project Template File | InstallShield | Flexera Software |
| .IVU | IMMERVISION ENABLES | Arquivos de desenvolvedor | ImmerVision XML User Interface | PURE Player | IMMERVISION ENABLES |
| .IWB | Ionic Wind | Arquivos de desenvolvedor | IWBasic Source Code File | IonicWind IWBasic | Ionic Wind |
| .IWS | JetBrains | Arquivos de desenvolvedor | IntelliJ IDEA Web Page | Internet Explorer | Microsoft Corporation |
| .IWZ | Flexera Software | Arquivos de desenvolvedor | InstallShield Express 2 Project File | InstallShield | Flexera Software |
| .IX3 | Lokasoft | Arquivos de desenvolvedor | Rebel Chess Program File | Rebel | Lokasoft |
| .IXX | Bjarne Stroustrup | Arquivos de desenvolvedor | C++ Include File | C++ | Bjarne Stroustrup |
| .IZS | Evrsoft | Arquivos de desenvolvedor | 1st Page 2000 JavaScript Example File | 1st Page 2000 | Evrsoft |
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