via: http://www.irradiatedsoftware.com/cinch/
Originally it comes with Windows 7 and it's one of these nice little Window Management features, where I would like to know, why apple missed to put it in OS X before.Take an Application Window (e.g. Safari) and drag it to the upper screen edge and it turns full screen. Drag it back and it turns back to the origin window size.
The other way: Drag the window to the left or the right screen edge and it fit to half screen size. Try this with two Finder Windows and you'll get something like Midnight Commander. Cinch places no Menu Bar item neither a Dock Icon, costs $7, and is absolutely worth a try.
