Particle life. Every particle is given one of a few types, and a randomly filled table says how strongly each type is drawn to or pushed away from each other type. That is the entire specification.
The table is deliberately lopsided, and that is the whole trick. If red chases green while green flees red, neither can ever settle, and the pair sets off travelling across the screen together. Add a third type and you get things that engulf each other, orbit each other, form chains, and split in two.
Make the table symmetrical, where every attraction is mutual, and all you ever get is clumps sitting still at equilibrium. The lopsidedness is what buys the motion.
The table comes from the seed, so a given seed always grows the same ecology and the seed next door grows a completely different one. Nothing here models chemistry. The resemblance to life comes from the asymmetry alone.