If you’ve ever wondered how best to kill a few hours, I have the answer. (Yes, I realize this is completely off-topic)
Desktop Tower Defense is incredibly addicting… The general idea is that you have to build up your defenses to stop the “creeps” from coming through.
Hint: diagonal lines of towers seem to work best.
If you’ve already done your 15 minutes of real work for the day, try out Desktop Tower Defense