The Harvard Network Accessible Dartboard
These guys hacked a dartboard to serve scores over a wireless network. There is an OpenGL client that grabs the scores, runs the games, stores the results in a database, and suggests moves based on player's past performance. On top of all this, the client looks exactly like the dartboard, so it can be projected over the real thing.
Not because I can play darts - I probably couldn't even hit the board - but because it's cool. I wonder if you could do something similar for a pool table. It would probably be quite a bit harder, as you'd need to be able to recognize each ball rather quickly. Maybe you could even build a program to recognize each ball and suggest the best shot and project it onto the table? Something new to do for these guys :-)
We do not live in the 21st century. We live in the 20 second century.