Tablets are still trying to find their place in the world. Are they productivity tools, media consumption devices, or are they all-purpose, do-anything magic slabs with a bevy of sensors and radios allowing you to unlock the powers of the universe? Air Display leans more towards the latter, turning your tablet into a secondary touchscreen display for Windows or Mac.
The app works via WiFi, which means that not only can you save a scarce video-out port on your machine, but you can also use the display from anywhere within WiFi range. Unfortunately you can't use your tablet's own on-screen keyboard to interact with your apps but Air Display can send touch input to the Windows OS.