Peter de Jong

Peter de Jong attractor — the same idea as Clifford's with the terms paired differently, and a different family of figures for it. Four knobs, an enormous space of shapes, and no way to predict which you will get.

x' = sin(a·y) − cos(b·x)
y' = sin(c·x) − cos(d·y)

It opens running, on the model selector, with its own knobs. Rotate it by dragging, zoom with the wheel, and turn the parameters to see what the figure does when the system changes.