They are less creatures than molecules. Now, mind you, as some complex sets of rules approach steady state I can pretend they are far-flung stellar empires with colors ascribed to each type of system of government (and have).

What is fooling you is the motion. This is sustained because the system has no conservation principles built in. You can make A-B pairs where B is attracted to A, A is repelled by B, and off they go, zoom. Were the meta-rules devised such that conservation of energy or momentum and such were baked in to whatever system you devised, you would see less exciting structures which would more resemble a late-stage pentamino explosion in the Game of Life.

With a sufficiently large processor, I would like to see this in three dimensions and more options for force, such as dropping off as the inverse of r or r-cubed or even r * log(r), or some "repulsive at a distance, attractive at very close quarters" particles. I have a feeling that such a system would grind to a halt even with clever optimizations.