Learn VIM by playing a Zelda-style game. Pretty amazing.
Deceptively simple, yet annoyingly addictive game where you roll a block around a grid-board and drop it through a hole. Seriously.
Desktop Tower Defense
Incredibly addictive online game. You place towers on your desk, and then lines of “creeps” try to run past them. If your towers are well-placed, they’ll shoot the creeps down. If not, they get across and you lose.