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 network transparency 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.

Homepage:
https://kde.org/applications/development/org.kde.kdiff3
