Gallon of pentagons
There are 15 kinds of convex pentagons that tile the plane. The gallon of pentagons is a collection of one dozen of each type. They are laser cut from solid hardwood, and lovingly packaged in a one-gallon freezer bag.
The set comes with a guide to the tiling patterns possible with each type and a brief write-up of the history and mathematics behind tiling pentagons. Super interesting; super challenging to play with.
When first sold on this site, each purchase of this set included a completeness guarantee: If a sixteenth convex tiling pentagon type is discovered, we would keep your set complete—just write us a note and we'd ship them out. In the intervening time, a proof has been issued that there are only these 15 types so the guarantee is now provided by mathematics, not by the proprietor.