Grail-o-matic: a customizable design you can use to make vases, cups, chalices, or even Tuscan pillars by rotating a profile you draw about an axis, as if on a lathe.
Part of the fun is designing your own Rubin vase illusion. See the faces in the negative space around the default design? You can make faceted columns as well as smoother cylinders by reducing the number of rotation segments.