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.