If you've ever wanted to turn your iPad or Android tablet into a secondary display, you can do so with this very neat application. iDisplay is an application which connects to your iPad or Android tablet via WiFi and then enables you to turn your tablet into secondary monitor.
I already have a 2 monitor setup so including my iPad I had 3 display setup. I could have also connected my Nexus 7 to make it a 4 display setup - pretty epic.
It's relatively easy to setup. All you need to do is buy the app on either (or both) your iPad or Android tablet, then download it on your computer or Mac, make sure you're on the same WiFi network and you're away. It's a very painless setup which literally takes a few seconds after you've downloaded all the apps.
As you can see above, I made my iPad my primary display which puts the dock at the bottom too. Obviously though there is slight lag and the frame rate is a lot lower than your desktop screens will be. So it probably isn't a good idea to use it to watch videos on. But it's actually very useful when keeping with your Twitter feed.