KDiff3 is a file and folder diff and merge tool which

  * compares and merges two or three input files or directories,
  * shows the differences line by line and character by character (!),
  * provides an automatic merge-facility and
  * an integrated editor for comfortable solving of merge-conflicts
  * has support for KDE-KIO (ftp, sftp, http, fish, smb),
  * has an intuitive graphical user interface,
  * provides a context menu for KDE-Dolphin and Windows-Explorer,
  * Support for many encodings and Unicode.

KDiff3 is a KDE Application
KDiff3 requires KDE Frameworks packages provided by Slackware