AllCast is an app allows Android users to stream content from their mobile devices to video game consoles, set-top boxes, and connected TVs, and it just made its debut in beta. Basically, it's like AirPlay for Android, as Gigaom pointed out.
The concept and execution is pretty straight forward. Find the content you want to view on your Android device, choose the "cast" button, and then select the device you want to send your content to. But because the app is still in beta testing, you'll have to be able to follow instructions in order to try it out.