It's the Solar System Simulator.
Imagine you're standing on Jupiter tomorrow morning at 10 AM. Being a naturally inquisitive space traveler, you're squizzing at Saturn through your telescope and thinking, hey, where's Cassini?
Since you happen to have a truly rockin wireless connection, you plug in your preferences to the Simulator and press Run, and bingo! You now know where to look (in the plane of the rings, a ways off to the right).
Go on, give it a go here. See if you can resist having a look at where Voyager 1 is now, when viewed from Earth (I recommend a 120 degree field-of-view).