Slime Mould
Every agent smells the trail at three points ahead of it, turns towards whichever smells strongest, steps forward and leaves more trail behind. That is the whole rule. The network is not in it. Put food down, wall the field off, or set a second and third kind loose, and the same rule finds a different answer.
Food, walls and rivals
Who follows whom
The kind on the left smells the kind along the top. Tap a square to swap between follows, ignores and avoids.
Paint on the canvas
Food pulls every kind towards it whatever the squares above say, and nothing crosses a wall. Painting the field costs some speed, and so does running more than one kind: the picture quietly goes coarser to pay for it and sharpens again when you clear back to one kind on a bare field.
Drag on the canvas to lay down trail, and the network grows towards your finger · open Food, walls and rivals to fence the field off or drop in a maze · F for fullscreen