Spectacle

Spectacle is a simple utility that allows you to easily organize your windows without using a mouse. Those familiar with similar apps will find Spectacle to be a simple and unobtrusive way to become more productive while using your Mac. Using Spectacle you can view multiple documents side-by-side, move windows to other displays, or even focus your full attention to a single task. If you happen to move a window without meaning to, it is also possible to undo or redo the last few actions.