Purpose: Brief intro to Tk
Tk is a Tcl extension, written in C, designed to give the user a relatively high level interface to their windowing environment. You can find the source code for Tk at http://sourceforge.net/projects/tktoolkit/ .
On a Macintosh, Tk provides some interfaces to the MacOS windowing system. On Microsoft Windows 95/98/NT/2000, Tk provides some interfaces to the Microsoft windowing system. On Unix and other platforms where Tk is available, Tk provides some interfaces to the X window system using a Tk specific look and feel, designed to look very similar to Motif, but not using the Motif libraries.
Tk was written by John Ousterhout, the creator of Tcl. A PostScript version of the paper introducing Tk to the world can be found at ftp://www.tcl.tk/pub/tcl/doc/tkUsenix91.ps . The PostScript for slides used by Dr. Ousterhout during various USENIX tutorials can be found at ftp://www.tcl.tk/pub/tcl/doc/tut.tar.Z .
Tk allows you to create, manage, and manipulate widgets, rectangular areas on the screen with various features, from which you can build quite powerful GUIs with little effort. Widget classes:
For sample images, look at Widgets in the initial Tk package.
There are many online Tcl and Tk tutorials, perhaps starting with an overview of tcl and tk; Tcl Tutor is quite popular as a desktop computer aided instruction application.
Also of interest might be Alternate toolkit bindings, Common Tk Error Messages and Possible Explanations, Alternate widget sets