Xbox Smartglass is a piece of software that’s meant to link your computer, tablet, or phone to the Xbox sitting under your TV. It’s actually a pretty impressive piece of software: it allows you to use your second screen as a information supplement to the main picture. One example is a map of Westeros as Game of Thrones plays on the television. Or, in a Wii U-esque move, it can display player information–like ammo, or health–while your Xbox displays a game. It lets you use your phone as a keyboard when using the Xbox’s Internet Explorer browser. In the future, Smartglass will have even more functionality, because Microsoft’s opened up its API to let third-party developers experiment with the software. If you’ve got an iPhone and want to try it out, tough luck; it’s still not available on iOS.
If you’ve got an Xbox and an Android Phone (running 4.0 or better), it’s a no-brainer. Go pick it up for free from Google Play.