Knot Theory knot puzzles and other knotty stuff.
Atomihedra  A structure with many amazing properties built up from PHn yeilds EHn yeilds AHn and NHn and which yeild Eduals that are space fillling.
A proof or counter example that Eduals will always fill space with other Eduals is needed. 
Electrihedra  This is the EH of the Atomihedron.  Made of injection molded plastic, an interesting and mind expanding puzzle.

KNOT ROBOT  A device that can tie knots and is a cool puzzle.  If a knot is its own mirror image then when you tie it twice it is untied!  Link to a coffee cup handle.  Now try to remove it.