Spotted this in comp.lang.smalltalk:

For those who have been following the articles and presentations I've been giving on ElastoLab, I've finally released the 3.0 version. In this version, the physics code has been completely re-written in Smalltalk. I did this because I had to fix some tough bugs in the physics and implement a new algorithm to handle multiple particle collisions with barriers. It was much easier implementing this in Smalltalk than in C . The performance in Smalltalk seems to be reasonable, so it wasn't worth keeping it in C .

Along with this release, Simberon will be holding a contest to win one of three Microsoft X-Boxes. The best three scenes submitted before the March 31st deadline win an X-Box. See the web site for details.

ElastoLab is a physics playground for kids age 9 and up that lets them play in a world with gravity, springs, elastics, and more. A simple scripting mechanism allows you to create simple games and interesting simulations.

ElastoLab is written in VisualWorks Smalltalk.

For more information, see Simberon's web site at http://www.simberon.com.

I can vouch for the coolness of ElastoLab - and not just for 9 and up - my nephew (who was 5 at the time) - was utterly fascinated by this!