.??_  Files ending in "_" are often compressed install files of the same
          name (e.g., .EX_ expands to .EXE, .DL_ expands to .DLL, etc.)
  .U    Unreal System File
  .U2   Telelogic Tau UML Model
  .U2E  Unreal Game Translation
  .U2P  Telelogic Tau UML Program Text File
  .U8   Raw Unsigned 8-Bit Audio Data
  .U96  EasyZip Temporary File
  .UAP  User Agent Wireless Telephony Profile
  .UAX  Unreal Audio File
  .UB   Audio File
        Raw Unsigned Byte (8-bit) Data
  .UC2  Compressed File
  .UCF  Xilinx Foundation User Constraint File
  .UCM  Urban Chaos Game File
  .UCN  Compressed Archive
  .UCS  Universal Classification Standard Database File
  .UDB  PINO 3-Server File
        Win2000 Uniqueness Database File (used in setup--provides answers that override defaults for unattended installs)
  .UDC  Acrobat Spelling File
  .UDF  MS Excel User Defined Function
        Photostyler Image Filter
  .UDL  MS Data Link
  .UDS  Sierra Generations Family File (program no longer supported)
  .UDW  Raw Unsigned DoubleWord (32-bit) Data
  .UE2  Encrypted Archive
  .UFO  Ulead Object File
  .UG   Drawing File (various)
  .UHA  UHARC Compressed Archive  [Download Link]
  .UHS  Universal Hint System File
  .UHTM  Unreal Tournament File
  .UI   User Interface
        Geoworks UI Compiler Espire Source
  .UIF  WordPerfect Long Prompts
  .UIH  Geoworks UI Compiler Espire Header
  .UIS  WindowBlinds Skin (changes the look and feel of WindowsXP)
  .UL   uLAW Audio File
  .ULD  Procomm Uploaded Files
  .ULP  Peugeot Diag 2000 File (vehicle diagnostic equipment)
  .ULS  Internet Location Service
  .ULT  UltraTracker Music Module
  .ULW  ULAW - Sun/NeXT
  .UMB  MemMaker Backup Archive
  .UMI  CDDB Database and PC Music Library in PlayCenter
  .UMOD  Unreal Self-extracting MOD File
        Unreal Tournament
  .UMX  Unreal Music File
  .UNI  MikMod (UniMod) Format
        Forcast Pro Data File
  .UNL  Informix Binary File Created by UNLOAD Command
  .UNQ  Fax View File (unverified)
  .UNR  Unreal Map File
  .UNX  Text File (usually UNIX)
  .UNV  BusinessObjects/WebIntelligence Universe File (End-user query analysis/reporting tool)
  .UOL  PhotoImpact Object Library File
  .UPD  dBase Update File
        ProUpdater Per/Directory Options Setting File
        Universal Print Driver (cross-platform)
        Updated Program Data (various)
  .UPI  ULead Photo Impact Program File  [XnView]
  .UPJ  ULead Project File
  .UPO  dBase Compiled Update File
  .UPR  FileMaker User Spelling Dictionary
  .UPX  ULead Photo Express Saved Image File
  .URF  Radar ViewPoint Universal Radar Format
  .URL  Internet Location
  .URT  Utah Raster Image  [XnView]
  .USA  Unreal Saved Game File
  .USB  D-Link FM Radio Update
        USB Protocol Analyzer Trace (USBChief, USBAdvisor, USBTracer)
  .USE  MKS Source Integrity File
  .USERPROFILE  Symantec Live Update User Profile
  .USL  LaserJet Landscape Font
  .USP  PageMaker Printer Font
        LaserJet Portrait Font
  .USR  User Database (various)
  .UTF  AOL Updating Files (found in TOD [Tools on Demand] folder)
  .UTL  Sound File
  .UTP  BinPatch Patch Data File
  .UTX  Unreal Texture File
        Unicode File (editor: UniPad)
  .UU   Compressed Archive File (UUENCODE)  [Tutorial]
  .UUD  Uudecoded  [Tutorial]
  .UUE  Uuencoded  [Tutorial]
  .UV2  Jane's Combat Simulations F-15
  .UVR  Ulead Cool 360 Viewer File
  .UVW  geoManager/geoInterface User View
  .UW   Audio File
        Raw Unsigned Word (16-bit) Data
        Unitype GlobalWriter File
  .UWF  UltraTracker Wave File
  .UWL  WordPerfect User Word List
  .UZE  Ultimate Zip Compresion Agent
  .UZR  UZR 3D Streamable 3D File Format