Turtletoy allows you to create generative art using a minimalistic javascript Turtle graphics API. You can only create black-and-white line drawings on a square canvas. By offering a very restrictive environment we not only hope to stimulate creativity, we also make sure that the turtles can (at least theoretically) be plotted using a simple plotter.
You can read the Turtle API reference first or directly start writing your own turtle here. Each turtle can be exported as SVG, suitable for high-res printing or a plotter.