While there is more to Logo than turtle graphics, I suspect drawing with turtles holds a special place in many of our hearts. With Berkeley Logo (ucblogo) under active development and available for modern operating systems (including OSX, Windows, and Linux), it feels like a natural fit for generating interesting shapes to plot on a modern plotter like the AxiDraw.
The Logo environment is designed to make it easy to jump in and get started drawing. In fact, something interesting to plot can be produced in a single line:
REPEAT 360 [ FD # RT 89 ]