If Google has their way, set top boxes and media centers will soon be a thing of the past, and instead you will use the devices you already have, but stream your content directly to your tv when you want to.
The Chromecast device is a HDMI Dongle you connect to your tv, the dongle connects to the internet, and the content you decide to push from your tablet, smartphone, or personal computer will magically appear on your tv at your bidding.
It was released yesterday and if you live in the United State you can order one right this moment. The Google Play store say they will ship the Chromecast devices in 2-3 weeks, but Amazon has already shipped the first units out. Time will tell when they will be available internationally.