4D Toys: a box of four-dimensional toys
There are several 4D games, but the one I found gave me the best grasp of the 4D world is this one [1], a puzzle in which you manipulate a hypercube.  You first play in 2D and 3D before going to 4D.  You end up with an intuitive understanding of 4D.<p>[1]  <a href="http://harmen.vanderwal.eu/hypercube/" rel="nofollow">http://harmen.vanderwal.eu/hypercube/</a>