By adjusting the arms, it can doodle different sorts of hypotrochoids. This is a fun LEGO project that both kids and adults will enjoy playing with. Everyone knows that drawing circles in this way is way too much fun.
If you want to try to make one just like it, the good news is that you can, because Allemann posted full instructions on his site JK Brickworks. This looks like a fairly easy build and it is easy to use too.