Many a time you may have applications or websites open that you may now want anyone else to see. The best thing one can do to hide such things from others is completely close the application itself.
For example you are watching a funny video at work and may not want your colleagues or far more worse you boss to catch you at it. This is definitely not the best solution as you will have to start the application back up again once they have left.
Hide Windows, Application Hider, Windows Hide