Komodo IDE is built on the Mozilla platform. It supports dynamic languages, including Tcl, Perl, PHP, Python, and Ruby; framework stacks like Ruby on Rails and CakePHP; and client libraries such as the Yahoo! UI Library and Dojo.
Komodo IDE is available for Linux, Mac OS X, and Windows platforms.
ActiveState introduced a free Komodo-based editor in January 2007 called Komodo Edit. See http://www.activestate.com/Products/Komodo_IDE for more information.
download for registered users only/FREE evaluation copy.
Information about other development environments can be found at IDE.
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/ .
Apparently, it could also be AOL's new Web browser: [L1 ]
[WK] Komodo's main advantage in debugging is that it keeps breakpoints correct when editing a file. In contrast with TclPro (and probably Tcl Dev Kit), this means that you don't have to move the breakpoints after you edit the files.