This is mgdiff, a graphical front end to the UNIX diff command based
upon X11R[456] and the Motif widget set. It allows the user to select
two files for comparison, runs the diff command, parses the output, and
presents the results graphically. This presentation can also be used
to generate a user-specified merge of the two files into a third file.

This program's appearance is based upon a program called gdiff, which
runs only on Silicon Graphics workstations and for which source code
is not provided.

WWW: https://BSDforge.com/projects/textproc/mgdiff/