My "hello world" for a new stack is always a version of Worm. Somewhere between Life and your Swarm, Worm wanders around looking for food and water, trying to avoid birds and other issues. Each round the worm survives it grows by a segment. If it doesn't get food or water, it is reduced a segment. And so on. Your Swarm is a few levels up from my iterations, totally inspirational! Thanks!