Mandelbrot set in multiple windows
The Mandelbrot set is probably the most famous example of fractals. This sketch is the most complex one here because it allows multiple windows to be open at the same time. When you click on the start button a window shows the complete Mandelbrot set, use the mouse to drag a box on the image to get an enlarged image of that area in a new window.
You can repeat this process in any of the open windows to further zoom into the set.