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:
http://sources.redhat.com/insight/ 
http://sourceware.org/insight

This is a sample screenshot from the Redhat site:
[http://sources.redhat.com/insight/screenshots/program-loaded.png]

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
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