Insight is a powerful frontend to gdb that uses Tcl/Tk. It was originally a commercial product written and sold by Cygnus. It is currently at version 6.8-1.

Since Cygnus was purchased by Redhat, it is now open source and available here:

This is a sample screenshot from the Redhat site:

It uses incr Tcl and [incr Tk] (included). It also includes Tcl/Tk 8.4.1. If someone is interested in updating it...

Jim Ingham's paper describing Insight (GDBTk)

Forked version of Insight, updated for modern versions of Tcl and optimized for Fortran: [L1 ]