You have the Apple TV that connects to your iTunes content. The Boxee that lets you record network TV on a virtual online DVR. TV makers like Samsung and LG have streaming apps built directly into their web-connected TV sets. And so on.
But at their core, none of these devices revolutionize television the way many are hoping Apple will if it ever launches its rumored television set. Most of these gadgets, the current Apple TV box included, function largely the same. You get access to the standard library of streaming services like Netflix and Hulu, plus the option to buy and rent movies and TV shows.