Tk is an extension to Tcl that allows you to quickly and easily build X11 applications that have the look and feel of Motif apps.
The TK-Shell is /usr/X11R6/bin/wish8.0
Native look and feel. The widgets have been rewritten to provide (nearly?) native look and feel on the Macintosh and PC.
Demo: /usr/X11R6/lib/tk8.0/demo/widget
Find the sources in tcl_new_spm.