A Graphical User Interface is a user interface that utilizes video graphics capabilities of a computer. Many toolkits for the creation of GUI's exist. In the Tcl world, Tk is one of the most commonly used, but there are Tcl bindings for other toolkits as well; see for instance Alternative GUI Toolkits.
[http://www.free-soft.org/guitool/%|%The GUI Toolkit, Framework Page] (alternates: [http://www.oocities.org/SiliconValley/Vista/7184/guitool.html] [http://wayback.archive.org/web/20091018195319/http://geocities.com/SiliconValley/Vista/7184/guitool.html]): a list of GUI toolkits from 2007 and before