| .TKP | MicroImages | Developer Files | MicroImages SML Script Standalone Application | TNTmips | MicroImages |
| .TLD | The Eclipse Foundation | Developer Files | Tag Library Descriptor File | Notepad++ | Don Ho |
| .TLH | Microsoft Corporation | Developer Files | Typelib Generated C/C++ Header File | Microsoft Visual Studio | Microsoft Corporation |
| .TLI | Microsoft Corporation | Developer Files | Typelib Generated C/C++ Inline File | Microsoft C/C++ | Microsoft Corporation |
| .TML | Odetics Broadcast | Developer Files | AIRO Timeline File Format | AIRO | Odetics Broadcast |
| .TMPL | Xfire, Inc. | Developer Files | Xfire User Interface Template | Xfire | Xfire, Inc. |
| .TNS | Texas Instruments, Inc. | Developer Files | TI-Nspire Document | Texas Instruments TI-Nspire Software | Texas Instruments, Inc. |
| .TOKEN | Microspot | Developer Files | Sandcastle Help File Builder Token File | Microsoft Sandcastle | Microspot |
| .TOM | Aptora | Developer Files | Total Office Manager Accounting Data | Total Office Manager | Aptora |
| .TPR | Pegasys | Developer Files | TMPGEnc Project File | Media Player Classic | Open Source |
| .TPT | Cerious Software | Developer Files | ThumbsPlus Thumbnail Template | ThumbsPlus | Cerious Software |
| .TPU | Borland | Developer Files | Turbo Pascal Unit | Turbo Pascal | Embarcadero Technologies |
| .TPX | DeLorme | Developer Files | DeLorme Topo Project File | Topo North America | Interscape |
| .TQS | Parasoft | Developer Files | Insure++ Data | Insure++ | Parasoft |
| .TR2 | Yadabyte | Developer Files | TomeRaider eBook File | TomeRaider | Yadabyte |
| .TRC | Microsoft Corporation | Developer Files | SQL Server Trace File | Microsoft SQL Server | Microsoft Corporation |
| .TRT | Galactix Software | Developer Files | Team Sports Scheduling System Report Template | Team Sports Scheduling System | Galactix Software |
| .TRU | Original Basic | Developer Files | True Basic Source | True Basic Bronze Edition | Original Basic |
| .TRX | Microsoft Corporation | Developer Files | Visual Studio Test Results File | Microsoft Visual Studio | Microsoft Corporation |
| .TS | Various Developers | Developer Files | Video Transport Stream File | Squared 5 MPEG Streamclip | Open Source |
| .TSQ | Microsoft Corporation | Developer Files | ODBC Script File | Microsoft ODBC Data Source Administrator | Microsoft Corporation |
| .TT | Microsoft Corporation | Developer Files | Visual Studio Text Template | Microsoft Visual Studio | Microsoft Corporation |
| .TTI | Delphi Softwares | Developer Files | Trojan File | Beast (Trojan Horse) | Delphi Softwares |
| .TTR | Interscape | Developer Files | TextTransformer Productions | TextTransformer | Detlef Meyer-Eltz |
| .TU | Holt Software | Developer Files | Turing Source File | Holt Software Turing | Holt Software |
| .TUR | Holt Software | Developer Files | Turing Program Source File | Microsoft Notepad | Microsoft Corporation |
| .TXG | ESRI | Developer Files | Georeference Subobject File | ERDAS Imagine | Hexagon Geospatial |
| .TXL | Open Source | Developer Files | TXL Source Code | Notepad++ | Don Ho |
| .TXS | Delphi Softwares | Developer Files | Beast (Trojan Horse) Data File | Beast (Trojan Horse) | Delphi Softwares |
| .TXX | National Library of Medicine | Developer Files | Insight Segmentation And Registration Toolkit Data File | Insight Segmentation and Registration Toolkit | Open Source |
| .TYB | Tyler Johnson | Developer Files | TY-Basic Source Code File | Ty-Basic | Tyler Johnson |
| .U2 | IBM | Developer Files | Telelogic Tau UML Model File | Rational Tau | IBM |
| .U2P | IBM | Developer Files | Telelogic Tau UML Program Text File | Rational Tau | IBM |
| .UAE | Interscape | Developer Files | WinUAE Configuration Data | WinUAE | Interscape |
| .UCLS | ObjectAid | Developer Files | ObjectAid UML Explorer Class Diagram | ObjectAid UML Explorer | ObjectAid |
| .UDD | Oleh Yuschuk | Developer Files | OllyDbg Module Information | OllyDbg | Oleh Yuschuk |
| .UDF | Open Source | Developer Files | Universal Disk Format Image File | 7-Zip | Igor Pavlov |
| .UI | Digia Oyj | Developer Files | User Interface File | Qt SDK | The Qt Company |
| .UIH | Geoworks Ensemble | Developer Files | Geoworks UI Compiler Espire Header | GEOS | GEOS |
| .UML | Visual Object Modelers | Developer Files | UML Data Object Model | Eclipse IDE for Java Developers | The Eclipse Foundation |
| .UMLCLASS | The Eclipse Foundation | Developer Files | UML Class Model | Eclipse IDE for Java Developers | The Eclipse Foundation |
| .UNX | Unknown Developer | Developer Files | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .USE | Unknown Developer | Developer Files | Log File | Microsoft Notepad | Microsoft Corporation |
| .USI | Sublime HQ Pty Ltd | Developer Files | UsiXML UI Description Data | Sublime Text | Sublime HQ Pty Ltd |
| .V | Microsoft Corporation | Developer Files | Subsampled Raw YUV Image | Microsoft Windows Media Player | Microsoft Corporation |
| .V2X | Texas Instruments, Inc. | Developer Files | TI Voyage 200 Macro | TI Connect | Texas Instruments, Inc. |
| .VAC | Ipswitch, Inc. | Developer Files | IMail Server Vacation Message File | Ipswitch IMail Server | Ipswitch, Inc. |
| .VAM | Microsoft Corporation | Developer Files | Visual Studio Common Tools Vanalyzer Project Item | Microsoft Visual Studio | Microsoft Corporation |
| .VAP | Dialogic | Developer Files | Dialogic Indexed Voice Audio File | Syntellect VoiceXML Studio | Syntellect |
| .VAR | M:Pact Technologies | Developer Files | Variable Data | My Personal Programmer | M:Pact Technologies |
| .VB | Microsoft Corporation | Developer Files | Visual Basic Project Item File | Microsoft Notepad | Microsoft Corporation |
| .VBA | Microsoft Corporation | Developer Files | Visual Basic For Applications Project | Microsoft Visual Studio | Microsoft Corporation |
| .VBI | IntelliCAD Technology Consortium | Developer Files | IntelliCAD VBA Script | IntelliCAD | IntelliCAD Technology Consortium |
| .VBP | Microsoft Corporation | Developer Files | Visual Basic Project File | Microsoft Visual Studio | Microsoft Corporation |
| .VBPROJ.USER | Microsoft Corporation | Developer Files | Microsoft Visual Studio Visual Basic Project User Options File | Microsoft Visual Studio | Microsoft Corporation |
| .VBR | Microsoft Corporation | Developer Files | Visual Basic Remote Automation Registration | Microsoft Visual Basic | Microsoft Corporation |
| .VBZ | Microsoft Corporation | Developer Files | Visual Basic Project Template | Microsoft Visual Basic | Microsoft Corporation |
| .VC | Software Arts | Developer Files | VisiCalc Spreadsheet | VisiCalc | Software Arts |
| .VC2 | Microsoft Corporation | Developer Files | Microsoft Visual C File | Microsoft Visual C++ | Microsoft Corporation |
| .VC4 | Microsoft Corporation | Developer Files | Visual C++ 4 File | Notepad++ | Don Ho |
| .VCH | Wholly Genes, Inc. | Developer Files | Master Genealogist Genealogy Chart | The Master Genealogist | Wholly Genes, Inc. |
| .VCL | Open Source | Developer Files | Varnish Configuation File | Varnish Cache | Open Source |
| .VCP | Microsoft Corporation | Developer Files | eMbedded Visual C++ Project File | Microsoft Visual C++ | Microsoft Corporation |
| .VCPROJ | Microsoft Corporation | Developer Files | Visual C++ Project File | Microsoft Visual Studio | Microsoft Corporation |
| .VCX | H+H Software GmbH | Developer Files | Virtual Disc Definition File | H+H Software Virtual CD | H+H Software GmbH |
| .VCXPROJ | Microsoft Corporation | Developer Files | Microsoft Visual Studio Visual C++ Project | Microsoft Visual Studio | Microsoft Corporation |
| .VDM | Overture Tool | Developer Files | VDM Specification File | VDM Tools | Overture Tool |
| .VDP | Microsoft Corporation | Developer Files | Visual Studio Deployment Project | Microsoft Visual Studio | Microsoft Corporation |
| .VDPROJ | Microsoft Corporation | Developer Files | Visual Studio Setup And Deployment Project | Microsoft Visual Studio | Microsoft Corporation |
| .VDT | General Electric Company | Developer Files | VersaPro Variable Declaration Table | VersaPro | General Electric Company |
| .VGC | ViziGen Ltd | Developer Files | ViziGen Code Generation Template | ViziGen | ViziGen Ltd |
| .VHD | Microsoft Corporation | Developer Files | VHDL Source File | Microsoft Notepad | Microsoft Corporation |
| .VHDL | Microsoft Corporation | Developer Files | VHDL Source File | Microsoft Notepad | Microsoft Corporation |
| .VIC | ViziGen Ltd | Developer Files | ViziGen Code Import Mappings File | ViziGen | ViziGen Ltd |
| .VIP | JKI | Developer Files | Virtual Instrument Package | JKI VIPM | JKI |
| .VIX | EditShare | Developer Files | Lightworks Video Index File | Lightworks | EditShare |
| .VJL | Microsoft Corporation | Developer Files | Visual J# Source Code | Visual J# | Microsoft Corporation |
| .VM | Apache HTTP Project Management Committee | Developer Files | Velocity Template | Apache Velocity | Open Source |
| .VOF | VZ Corporation | Developer Files | VZ Programmer Object Folder | VZ Programmer | VZ Corporation |
| .VPC | ViziGen Ltd | Developer Files | ViziGen Configuration File | ViziGen | ViziGen Ltd |
| .VPI | Open Source | Developer Files | Virtual Pascal OS/2 Unit File | Virtual Pascal | Allan Mertner |
| .VPW | Wheat Stone | Developer Files | VoxPro Database File | VoxPro | Wheat Stone |
| .VSCT | Microsoft Corporation | Developer Files | Visual Studio Command Table | Microsoft Visual Studio | Microsoft Corporation |
| .VSIXMANIFEST | Microsoft Corporation | Developer Files | VSIX Manifest | Microsoft Visual Studio | Microsoft Corporation |
| .VSK | Microsoft Corporation | Developer Files | Microsoft Development Common IDE File | Visual Studio IDE | Microsoft Corporation |
| .VSMACROS | Microsoft Corporation | Developer Files | Visual Studio Binary Macro Project | Microsoft Visual Studio | Microsoft Corporation |
| .VSMPROJ | Microsoft Corporation | Developer Files | Visual Studio Text Macro Project | Microsoft Visual Studio | Microsoft Corporation |
| .VSP | Corel | Developer Files | VideoStudio Project File | Corel VideoStudio Pro | Corel |
| .VSPS | Microsoft Corporation | Developer Files | Visual Studio Serialized Performance | Microsoft Visual Studio | Microsoft Corporation |
| .VSPX | Microsoft Corporation | Developer Files | Visual Studio Performance Report File | Microsoft Visual Studio | Microsoft Corporation |
| .VSSSCC | Microsoft Corporation | Developer Files | Visual Studio Solution Source Control File | Microsoft Visual Studio | Microsoft Corporation |
| .VSZ | Microsoft Corporation | Developer Files | Visual Studio Wizard File | Microsoft Visual Studio | Microsoft Corporation |
| .VTM | Adobe Systems Incorporated | Developer Files | Visual Tool Markup Language Document | Adobe Dreamweaver | Adobe Systems Incorporated |
| .VU | Sony | Developer Files | Playstation 2 VU Development Source Code | PlayStation 2 | Sony |
| .VUP | Microsoft Corporation | Developer Files | Microsoft Visual Studio Visual C++ Utility Project File | Microsoft Visual Studio | Microsoft Corporation |
| .VWL | PTC | Developer Files | Vuforia Word List | PTC Vuforia | PTC |
| .W | Progress Software Corporation | Developer Files | OpenEdge Architect Source Code File | OpenEdge | Progress Software Corporation |
| .W3 | APL2000 | Developer Files | APL+Win Workspace File | APL+Win | APL2000 |
| .W32 | Microsoft Corporation | Developer Files | Win32 Makefile | GNU Make | GNU Operating System |
| .WAM | Team17 | Developer Files | Worms Armageddon Mission File | Worms Armageddon | Team17 |
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