The beta of the Boxee media center application is available for the Apple TV again, but like earlier versions, it's still a hack since Apple doesn't officially support adding extra software to its home media center appliance.
Boxee had been available for Apple TV while the application was still in the alpha testing phase, but was temporarily dropped with the release of the Boxee beta version at the end of 2009.
Boxee lets users stream Internet content, including TV shows and movies, to their computer or TV. It also supports playing content that's already on your Mac or PC.
Installing Boxee on Apple TV involves a few steps and an USB thumb drive, but isn't an overly complex process. Instructions are available at the Boxee Support Web site.
Boxee is free and available for download at the Boxee Web site.