The good people at Freeverse are savvy to this, but they figured why bother creating individual applications with a full screen mode when you can create an app that'll let any app have a full screen mode of sorts. Thus Think was born.
Think has a very cool Illumination Panel that allows you to pick from any of your currently running applications. As soon as you pick an app, Think throws up a backdrop (the color is up to you, though it defaults to black) that covers up the rest of your desktop (on your main monitor as well as any secondary monitors you might have) though the Dock remains visible. Think goes one step further and displays the icon of the currently focused app in its Dock icon, just in case you forget.
It is obvious that Freeverse spent some time thinking about this application. Now, what would you expect to pay for such an application? If you said nothing, not only are you cheap but you're also correct! That's right, Freeverse is giving this gem away (Mac OS X 10.4.3 or later is required).
Check out the gallery below for some screenshots.