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