Komodo is a Mozilla-based cross-platform cross-language IDE created by ActiveState.
See http://www.activestate.com/Products/Enterprise/ASPN_Komodo/ for more information.
Information about other development environments can be found at IDE.
Among the many interesting particular features of Komodo is the "ActiveState GUI Builder", a "simple tool for creating Tk-based GUIs for Perl, Python, and Tcl".
See also GUI Building Tools.
Features specifically related to Tcl are
You can see recorded webcast demos of Komodo at http://www.activestate.com/Corporate/Events/Webcasts/ .
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