Ghostzilla is a Web browser like Firefox, but it shows up and disappears instantly, discreetly, blended with your application -- any application -- so the Web pages look like part of it and not like the Web at all. (Read here how.)

What would you use it for?

Hide from your boss and coworkers. Not a good idea: you can get fired (the network administrator sees everything you do) or end up wasting lots of time instead of dealing with what bothers you.
Survive endless meetings (if you have a laptop; kind of like (1) but a little better).
Have a browser instantly available and dismissable within your work application, washed out from ads and unnecessary pictures. This sounds useful -- except it will help you develop that attention deficit disorder. Seriously.

So what's it for then? - Entertainment. Ghostzilla is a form of computer art

The Ghostzilla window disappears when the mouse cursor is moved away from it, letting the user easily hide it.
The user can set the preferences to set security (hiding) levels. For example: He can display no images unless the mouse is put over it (they stand out, thus making it more easily recognized as the Web), or display plain grey text on a white background

The license of this software is Freeware, you can free download and free use this web browser software.