Created by Ernst Uys, Sablo for iOS lets you explore the boundary between order and chaos using the Abelian Sandpile model (also known as the Bak–Tang–Wiesenfeld model in theoretical physics). This algorithmic model is a cellular automaton that approximates the dynamics of a pile of sand grains on a regular lattice and is known to exhibit the phenomenon of self-organized criticality, which Ernst explains to CAN, is when a dynamical system shows algebraic long-range correlations. It is one of the mechanisms by which complexity arises in nature.
Each site on the lattice contains a number of "sand grains". If this number exceeds a certain threshold, all the grains on that site are redistributed to its neighbouring sites on the lattice. This simple rule has complex consequences. The addition of a single grain of sand to a site can have no effect; it can result in a highly ordered pattern; or it can induce complex patterns that cascade throughout the lattice, veering between order and chaos. Periodic patterns in both one and two dimensions can result. Certain one dimensional patterns, called "strings", can merge and split and have a "momentum-like" property that is conserved in interactions between them.