Wikipedia
Kompare
Kompare (formerly "Kdiff") is a graphical diff tool targeting developers. It allows users to compare two different text files or two directories. It is part of the KDE Software Compilation and therefore primarily used on Linux and other Unix-like operating systems, as well as Microsoft Windows. Kompare does not actually compute the differences between the compared files itself, but is merely a graphical front end to the command line interface diff utility.
It is a standard KDE SC tool, it comes packaged with the kdesdk module.