The Smalltalk language in it's natural and object-oriented style is a nice language to develop simulations. Today Yoshiki Ohshima announced his Kedama project - a parallel particle programming system. Kedama is deeply inspired by StarLogo and StarSqueak.
It requires a special VM plugin which is already provided for the windows version. If you run Squeak on other platforms you can easily build the plugin using the given changeset. Look at his website for the changeset, the plugin and some examples like a gas tank or forest fire simulation.