Tcl (Tool Command Language) is used by over half a million developers worldwide and has become a critical component in thousands of corporations. It has a simple and programmable syntax and can be either used as a standalone application or embedded in application programs. Best of all, Tcl is open source so it's completely free.
Tk is a graphical user interface toolkit that makes it possible to create powerful GUIs incredibly quickly. It proved so popular that it now ships with all distributions of Tcl.
Tcl and Tk were created and developed by John Ousterhout. Developers all over the world followed his example and built their own Tcl extensions. Today, there are hundreds of Tcl extensions for all manner of applications.
Tcl and Tk are highly portable, running on essentially all flavors of Unix, (Linux, Solaris, IRIX, AIX, *BSD*, the list goes on and on) Windows, Macintosh, and more.
Code Sample
# Tk as a loadable package
package require Tk
# define a button called 'hello' with it's 'text' and 'command' properties set.
# the '.' refers to the root widget.
button .hello -text "Hello, World!" -command { exit }
# place button hello into the root widget/window
pack .helloThis places a clickable button on the screen, labeled "Hello, World", and the application terminates when the button is clicked.
To run this you would place the sample into a file (foo.tcl) and issue:
$ tclsh foo.tcl
in your shell.