Insight is a powerful frontend to gdb that uses Tcl/Tk. It was originally a commercial product written and sold by Cygnus.
Since Cygnus was purchased by Redhat it's now open source and available here: http://sources.redhat.com/insight/
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) http://www.usenix.org/publications/library/proceedings/tcl2k/full_papers/ingham/ingham_html/index.html