Obviously this has nothing to do with -why- Apple killed Front Row, but there is an excellent alternative coming out soon called Squire. I've been running the beta for a while and it is shaping up to be a great front row replacement.
Plex and Infuse are apps that allow you to stream your movies, tv shows or videos from a local NAS or PC. Plex requires more stress on the computer by transcoding the video to make it compatible with the Apple TV. Infuse has the ability to stream the computer. Alex required it's server app to be running, it's personal preference to be honest but i'm using Squire allows you to stream from torrent's Mac only and required a Server app running & Infuse both are great but if you're running a large library i heard Plex is better. Any other questions i'm sure the we can help out.
Basically its a feature called Streams that allows you to add sources from the internet basically integrating them in your library. They're like plugins. I honestly do not know how the backend works but i would guess it works a little like popcorn time whereas your computer is downloading the torrent and the Apple TV is displaying the stream. Its a little better explained on their website at http://www.squireapp.com scroll down to where it says Streams.
I use Squire pulls Movies and TV shows from torrent APIs using something called streams. They have a iOS app, Apple TV App and OS X application.
Drawback of this application requires a helper app to be installed on a Mac in order for the entire thing to work however 100% recommend if you're looking for a better Media Center that doesn't require local files.
Nevertheless it's a pretty solid Application I'd highly recommend looking on there website for a better understanding.