Meld is a visual diff and merge tool.

You can compare two or three files and edit them in place
(diffs update dynamically). You can compare two or three folders and launch
file comparisons. You can browse and view a working copy from popular version
control systems such such as CVS, Subversion, Bazaar-ng and Mercurial.

This one uses GTK+3 instead of GTK+2.

NOTE: This package conflicts with the previous version of meld.
Only install one of them, but NOT BOTH.