Appnr

compares and merges 2 or 3 files or directories

KDiff3 compares two or three input files and shows the differences
line by line and character by character. It provides an automatic
merge facility and an integrated editor for comfortable solving of
merge conflicts. KDiff3 allows recursive directory comparison and
merging as well.

This is the standard version of KDiff3, highly integrated into KDE.
It has got KIO support (allowing for remote access of files and
direct access to files in compressed archives) and integration into
konqueror's context menu. There's also a stripped-down version called
kdiff3-qt not depending on the KDE libraries.