xxdiff is a graphical tool for viewing the differences between two or three
files, or between two directories, and can produce a merged version thereof.

Some of its features:

  - Comparing two files, three files, or two directories (shallow and
    recursive)
  - Horizontal diffs highlighting
  - Files can be merged interactively and resulting output visualized
    and saved
  - Has features to assist in performing merge reviews/policing
  - Can unmerge CVS conflicts in automatically merged file and display
    them as two files, to help resolve conflicts
  - Uses external diff program to compute differences: works with GNU
    diff, SGI diff and ClearCase's cleardiff, and any other diff whose
    output is similar to those
  - Fully customizable with a resource file
  - Look-and-feel similar to Rudy Wortel's/SGI xdiff; it is desktop
    agnostic (i.e. will work equally well with KDE or GNOME)
  - Features and output that ease integration with scripts

WWW: http://furius.ca/xxdiff/