http://www.swarm.org/wiki/Main_Page
I don't remember much, just that it was a nice language, well fitting for the problem domain. It seems meanwhile they also added Java and C++ support.
Off-topic, but if you are interested in frameworks like this, also check out the MASON Multiagent Simulation Toolkit (which is based in Java):
http://www.cs.gmu.edu/~eclab/projects/mason/