Roach Rash is a little and neat 3D casual game. Visit http://www.creatorum.org/ to download version suitable for your system.
This game is absorbing in a good way and yet meditative. It's just what you need to relax for a couple of minutes and then return to your business with renewed energy.
It's so simple that you'll get the point in a second. At the same time it's worth playing for months to improve your skill. No control keys, no mouse clicking - use just a few careful mouse movements to destroy insidious insects. Dead reckoning and mind presence are your weapons. There is no excess in this game, but all that is necessary is there. Just try it, and you'll see it stands out against ordinary arcades.