Starting with a character: : U

File extension	Full name
U File Extension	Unreal Tournament Class Package
U10 File Extension	UFile 2010 Tax Return
U11 File Extension	UFile 2011 Tax Return
U12 File Extension	UFile 2012 Tax Return
U3D File Extension	Universal 3D File
U3I File Extension	U3 Application Information File
U3P File Extension	U3 Smart Application
U8 File Extension	3D Lemmings Audio File
UAX File Extension	Unreal Audio Package
UB File Extension	Unsigned Byte Audio File
UBJ File Extension	Universal Binary JSON File
UBOX File Extension	Universe Sandbox Data File
UC File Extension	UnrealScript Class
UC2 File Extension	UltraCompressor 2 Archive
UCCAPILOG File Extension	Microsoft UCC API Log File
UCE File Extension	Windows UCE System File
UCF File Extension	WebEx Media File
UCI File Extension	UFS Explorer Backup File
UCL File Extension	Unreal Tournament cache file
UCM File Extension	Crazy Machines Model File
UCT File Extension	UC Browser Theme File
UD File Extension	OmniPage User Dictionary
UDB File Extension	Dynamics AX User Database File
UDC File Extension	Adobe InDesign User Dictionary
UDCX File Extension	Universal Data Connection File
UDEB File Extension	Debian Package File
UDF File Extension	Universal Disk Format File
UDK File Extension	Unreal Engine Map File
UDL File Extension	Microsoft Universal Data Link File
UDS File Extension	FIMware database file
UEA File Extension	Protector Suite QL Encrypted Archive
UFO File Extension	Ulead File Object
UFR File Extension	Ultra Fractal File
UFS File Extension	FreeBSD Unix File System File
UFSUZIP File Extension	Compressed Unix File System File
UHA File Extension	UHarc Compressed Archive
UHTML File Extension	uHTML document file
UI File Extension	User Interface File
UIBAK File Extension	UltraISO Backup Disk Image
UIF File Extension	Universal Image Format Disc Image
UIS File Extension	WindowBlinds User Interface Specification
UKX File Extension	Unreal Animation Package
ULAW File Extension	Raw u-Law Audio File
ULF File Extension	Universal List File
ULS File Extension	NetMeeting User Location Service File
ULT File Extension	UltraTracker Module
ULW File Extension	u-Law Audio File
ULZ File Extension	USBlyzer Data Capture File
UMF File Extension	MediaHolder Universal Media Format File
UML File Extension	UML Data Object Model
UMLCLASS File Extension	UML Class Model
UMOD File Extension	Unreal Tournament Module File
UMS File Extension	Rune 3D Mesh File
UMX File Extension	Deus Ex file
UNAUTH File Extension	SiteMinder Unauthorized Message File
UNI File Extension	MikMod UniMOD Module
UNITY File Extension	Unity Scene File
UNITY3D File Extension	Unity Web Player File
UNITYPACKAGE File Extension	Unity Package File
UNK File Extension	UVProbe file
UNKNOWN File Extension	Unknown File Type
UNL File Extension	Garmin Unlock File
UNR File Extension	Unreal Level Map
UNT File Extension	AutoCAD Unit Definition File
UNX File Extension	Unix Text File
UOF File Extension	Uniform Office Document
UOP File Extension	Uniform Office Presentation
UOS File Extension	Uniform Office Spreadsheet
UOT File Extension	Uniform Office Document
UPD File Extension	Program Update Information
UPDATE File Extension	ISAPI Update File
UPDATR File Extension	iConomy Update File
UPF File Extension	Nokia Phone digital photo file
UPG File Extension	Firmware upgrade file
UPK File Extension	Unreal Engine 3 Package
UPOI File Extension	iGO Points of Interest File
UPR File Extension	FileMaker user spelling dictionary
UPX File Extension	Ultimate Packer for eXecutables File
UQM File Extension	The Ur-Quan Masters Game Data File
URL File Extension	Internet Shortcut
URR File Extension	Uniface Signatures File
URT File Extension	Utah Raster Toolkit File
USA File Extension	Microsoft Office headers file
USEQ File Extension	USeq Genome Data File
USER File Extension	Visual Studio Project User Options File
USERPROFILE File Extension	Norton Antivirus User Profile File
USERTILE-MS File Extension	Windows 8 User Tile File
USF File Extension	Nintendo 64 Music File
USFLIB File Extension	Nintendo 64 Song Library
USM File Extension	USM Game Video File
USR File Extension	FileMaker Pro Database File
UST File Extension	WiFi SiStr exported user theme file
USTAR File Extension	Uniform Standard Tape Archive Format File
USX File Extension	Unreal Static Meshes
UT2 File Extension	Unreal Tournament Map
UT2MOD File Extension	Unreal Tournament 2003/2004 Module File
UT3 File Extension	Unreal Tournament 3 Map File
UT4MOD File Extension	Unreal Tournament 2004 Module
UT8 File Extension	Ghost Master Language File
UTC File Extension	Bioware Creature File
UTF8 File Extension	Unicode UTF8-Encoded Text Document
UTW File Extension	Unity Whirld File
UTX File Extension	Unreal Texture Package
UTXT File Extension	Unicode Text File
UTZ File Extension	UIQ Theme Package
UU File Extension	Uuencoded File
UUD File Extension	UUDecoded File
UUE File Extension	Uuencoded File
UVF File Extension	Uncertain Value Format
UVX File Extension	Unreal Tournament 2003 Saved Game
UW File Extension	Unsigned Word Audio File
UWF File Extension	UltraTracker Wave File
UWL File Extension	User Word List File
UXX File Extension	Unreal Tournament Cache
UZIP File Extension	FreeBSD Compressed Disk Image