Aggregate was initially intended to be a simulation of diffusion limited aggregation. Essentially, you release sticky particles into a container and let them take random walks until they stick to something. Clusters form that have predictable properties. This started out as something like that, but then the particles acquired momenta, and the clustering points became massive. So I had a little space with massive bodies wandering around with random perturbations, sticking to things and whatnot. Anyway, the goal was to generate pretty pictures, and I believe I have accomplished that. Aggregate now has a "Space File" format so you can build spaces containing attractors and particle sources. It's robust, but somewhat difficult to use.