tkmerge is a tk script to help with the task of merging the differences
between two files.

On startup creates a window consisting of four panels. One for each
of the source files, one for the merged result, and a fourth that can
contain substitution text (which is user editable) and various selection
and navigation buttons and options.

Additionally, for any of the difference sequences you may elect to
edit them with your favorite editor via the "Editor" button.