<a href="http://www.sno.phy.queensu.ca/~phil/exiftool/" target="_blank">ExifTool</a> by Phil Harvey.
ExifTool is the real "engine", but as it is a command-line tool it is to some users less userfriendly. jExifToolGUI is built around exiftool and tries to give a lot of funtionalities and flexibility without you having to remember every command line parameter. jExifToolGUI only implements part of the functionality of ExifTool. It is definitely not a complete GUI for Exiftool and can certainly not replace it (