In the spirit of designing fun, this is a 3D tic tac toe board that I made under the direction of a math professor at Missouri University. Designing for fun is a really interesting problem because it requires identifying the moments that make a game entertaining. 

Compare this to the usual 2D 3×3 board game. That is a game that might have been interesting the first few times you played, but rapidly loses fun once it is solved. It is easy to determine the optimal play in every case, which makes it a game with little leeway for mastery. Making the game 4×4 doesn’t do much to help, as the restrictions in dimension makes it almost impossible for anyone to actually win.

Expanding to 3D is an instant improvement. Note that it is a 4x4x4 instead of a 3x3x3, as in the latter case, the first player should always choose the middle space, which immediately constrains all possible moves for the second player. The 4x4x4 makes the game almost impossible to solve by hand. The first move can be responded to with any space in the board. Furthermore, most moves leave enough possibilities for future moves that the game never becomes deterministic. The transparent design is ideal as it is possible to visually see every possible 4-in-a-row angle, making the entire gaming experience transparent, which causes wins to be even more surprising. Winning and losing both feel fair and fun, as spotting that winning move is entertaining for both players and neither player feels like they were cheated by the game mechanics.