The KDiff3

KDiff3 is a file and directory diff and merge tool which

compares and merges two or three text input files or
directories,

shows the differences line by line and character by
character(!),

provides an automatic merge-facility,

has an editor for comfortable solving of merge-conflicts,

provides networktransparency via KIO,

has options to highlight or hide changes in white-space or
comments,

supports Unicode, UTF-8 and other file encodings,

prints differences,

supports version control keyword and history merging.