Shade inactive windows in Mac OS X with HazeOver
If you get easily distracted by things sitting around in the background, HazeOver might be for you. It’s a free utility that casts a shadow on all inactive windows, in other words, any window that isn’t in the foreground will be “hazed over.” Windows actually phase in and out of the shadow so it’s a neat effect even if you aren’t using it to minimize distraction and just want some additional eye candy on your Mac.
Oh and if you use multiple monitors on your Mac, it will only cast shadows on your primary display, but the developer is working to fix that bug.
You can download HazeOver for free from the developers site.