Did you ever feel like rolling something nicely on a level surface but you are bored of using spheres and cylinders? Well then, we got the perfect answer for you, solids of constant width. These are solids which when rolled over a level surface have their geometric center at a constant height in all situations.
Oloids happen to be a quite famous and rather artsy example as of such a solid. An Oloid is a three-dimensional curved geometric object that was discovered by Paul Schatz in 1929. It is the convex hull of a skeletal frame made by placing two linked congruent circles in perpendicular planes, so that the center of each circle lies on the edge of the other circle. The distance between the circle centers equals the radius of the circles. While it may look complex it is actually pretty easy to model. Another interesting family of solids is the steinmetz solids which is a solid obtained from the intersection of two or three cylinders of equal radius at right angles to each other and one can also see that these roll too.
Read more here on Wikipedia.
A really nice animation of the oloid on YouTube.
Oloids and more.
Steinmetz solid in action.
About that Steinmetz solid.