Also known as iTk.
Megawidget framework based upon (and requiring) incr Tcl.
CVS Repository at http://sf.net/projects/incrtcl/ , with some documentation, etc. also available at http://purl.org/tcl/package/itk/ .
Current tar files have itk included with itcl. This will change if/when someone in the itcl community completes work on the TIP to bundle itcl in with Tcl.
See also incr widgets/iwidgets.