There is a little strategic gem to buy at Humble Introversion Bundle: Darwinia. Hurry up, there are only 24 hours left … until you have to buy the game elsewhere … where you can’t set the price.
The goal of the game is to help little 2D people (the Darwinians) recapture their artificial world after a nasty virus infection. It’s not too easy and not too hard, the graphics is simple, the controls are easy to master.
I also tried Uplink (same producer) but the game is a little bit too text-heavy to blast off some steam after work.