What is Aereo?
Aereo bills itself as "live TV, wherever you are, whenever you want." Basically, the service lets you watch broadcast channels — CBS, NBC, Fox, ABC, the CW, and more — live on a browser (like Chrome or Firefox), on an iPhone or iPad, or on TV-connected devices like Apple TV and Roku. Furthermore, you can record shows à la DVR and save them to watch later — everything from, say, Parks and Recreation to Saturday Night Live to Monday Night Football. Cable channels are not included.

How does it work?
Typically, broadcast channels are available to anyone with a TV antenna or satellite dish on top of their home. Aereo subverts this by cramming hundreds of thousands of tiny antennas into a remote storeroom in a densely populated city. So, if you're using Aereo to secretly watch a baseball game on your computer at work, you're basically streaming the game directly from one of these itty-bitty antennas a few miles away.

Where is it available?
For now, just metropolitan New York. But the people behind the service say they plan on expanding nationwide to big cities like Austin, Chicago, Miami, and Washington, D.C. — each of which would have an antenna-packed storeroom of its own. (Click here to see if your city is included.)

Is it free?
No. Subscribers pay $8/month (or $80/year) to essentially "rent" one of the mini antennas.

And this is legal?
Yes, at least according to a federal appeals court ruling earlier this month. The court rejected a request from broadcasters (including Disney, CBS, and News Corp.) to stop Aereo from streaming their content. According to All Things D, "the court said that Aereo's technical architecture — which pulls down broadcast TV signals from the air… and retransmits them to its users over the web, without paying the broadcasters for the rights to do so — may well hold up to further legal scrutiny." Since each customer gets their own remote antenna, "it's analogous to legally-sanctioned 'rabbit ears' that enhance broadcast signals in the home," says The Verge

But the networks aren't happy, right?
Not one bit. On Tuesday, News Corp. threatened to pull Fox off the airwaves and move it to cable if Aereo prevails in court, claiming that the start-up is threatening the network's ability to sell advertising. "Aereo is stealing our signal," said News Corp. chief operations officer Chase Carey. "We are going to pursue our legal rights. And we believe we will prevail."

Update: An earlier version of this story used Monday Night Football as an example of programming you can stream via Aereo. As a commenter points out, that is not the case, as it airs on ESPN. The author clearly doesn't watch enough football.