MandalaGaba is a drawing board that specializes in mandalas and other artistic mathematical magic. Click and drag and watch what happens! You can save and share your work; the creators have a blog and an instagram featuring quality examples.
After radial symmetry (mandalas) and tessellations, I just finished implementing recursive drawing. Do tweak the buttons & sliders, seeing their effect on a pen stroke is the best way to understand what they do. I hope this is fun.