(This entry is intended to be the quick "you have 30 seconds to explain Tcl to someone" speech.)
Tcl is a rapid-prototyping environment. It is most known as a scripting language, but Tcl is much, much, more. Tcl has been adapted to run webservers, robotic manufacturing equipment, and even monitor spacecraft. Tcl is bundled with every major Linux distro, OS X, even Cisco routers. It also runs under Microsoft Windows. Odds are that you have probably used a Tcl/Tk application and never even knew it. (If you've watched NBC since 1998, you've seen the results of a Tcl application on screen.)
All this power may sound a little daunting to learn. No worries; Tcl is extremely simple to program. There are but 12 rules a coder needs to be familiar with to competently program in it. This power and simplicity makes it an essential tool for many systems.
If all that were not enough, Tcl has a powerful GUI construction tool called Tk. Tcl/Tk quietly runs a lot of day-to-day utilities under Linux. If you've ever compiled the kernel using Xconfig, that's a Tk app.
Where can I get Tcl/Tk?
With the notable exception of Microsoft Windows, if your computer can read this web page, it probably has Tcl/Tk installed. To get started programming, go out to a command line and type "wish". Running Windows? Don't have Tcl/Tk? Have an older version? No problem, for our friends at ActiveState have friendly bundles of Tcl and other tools (both open source and ActiveState commercial) for Microsoft Windows, MacOS X, Solaris, and Linux. The bundle includes an up-to-date Tcl/Tk interpretor, a lot of popular packages, and most of the tools you would need to get started on your own killer app.
WJP 2007-05-21. It seems to me that it would be useful to name the Tcl app seen on NBC, maybe even give a URL or screen shot.
DKF: I don't think you normally see the application; just its output.
LV Well, once someone steps forward to start updating and maintaining that web site, it seems like it would fit into an intro to tcl.
- SDW Cliff is working on giving me access as part of the preparation work for the '08 Conference
TJK You should also point out (i.e., emphasize) the open nature of the use and distribution license in a 30-second overview.
Just vaguely related to the title, but Elevator simulation could be demonstrated in that context... :^)