Check out gibell's Reuleaux solids
too. Those are surfaces of rotation based on Reuleaux polygons, which are curves of constant width. These are also surfaces of constant width, but not
surfaces of rotation. So despite looking decidedly non-spherical, they roll smoothly as spheres.
There are two different Meissner solids, subtly different. Look closely at the edges. Some are rounded and some are sharp. One of them has the round edges making a a triangle and the sharp edges meeting at a point; the other has them the other way around.
These are sized for compatibility with gibell's solids, so if you get all five they will all roll smoothly under the same flat surface together. And like gibell's, they are hollow with internal braces to lend extra support, with holes in the bottom to let the support material out.
Printed great. Video below! (the two foreground shapes are mine; the red one in the background is one of gibell's from the set linked above)