Take the basic idea of cellular automata, like Conway's life. Then apply the rules at each level of detail, making sure your neighbourhood includes the nearby cells in the higher and lower level of details.
The world is continuous in space and time, and the results are usually dynamic fractals, which can look quite real.
A useful property of these automata is that they can be approximated at any detail level, making them useful in video games for example.
This video shows the same algorithm being applied using the same neighbourhood but different mappings. There are 2^(2^17) mappings to choose from, so quite a big search space.
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