Whiteboard turns any iPhone into a virtual sketchpad, allowing you to quickly rough out images using the your finger on the touch screen. Users can choose from a set of standard colors with the option of changing pen sizes. An eraser is also available. Consider it the latest version of the "back of the napkin" sketch.

But the real magic happens when two Whiteboard users come into close proximity of one another. Using the built-in wi-fi functionality, Whiteboard gives users the option to wirelessly tether two handsets together. The result? A collaborative sketchpad where users can draw on the same surface - even if they're across the room from one another.

Our expectations weren't high. We expected some lag between drawing on one surface and having it appear on the other iPhone. But we were pleasantly surprised. The app is incredibly responsive. Watching the drawings on one iPhone almost instantaneously replicated on the other user's screen is, if nothing else, entertaining. And entertainment is most likely going to be the most prevalent use.

Granted, using Whiteboard to sketch wireframes before your big client meeting or drawing a quick diagram of a process for your colleague are all perfectly reasonable and serious uses of the tool. But it's far more likely that - as fun as the app is to use - you'll find yourself using Whiteboard to engage in games of Tic-Tac-Toe and Dots & Boxes with colleagues during meetings.

Whiteboard is a free application. To try it, download it from the App Store or search for "Whiteboard: Collaborative Drawing" from the App Store on your iPhone.