The Apple TV jailbreaking scene is maturing at a significant pace. We've already seen our first third-party app following the greenp0ison jailbreak, which was quickly followed by a demo of the Plex media center and some experiments with making it work with Wiimotes.
Now, respected hackers of the original model Apple TV Fire Core are showing off its modified software, aTV Flash, running on the Apple TV 2G. Our own TJ Luoma was impressed by aTV Flash when he tried it on an older model Apple TV; it adds support for streaming all sorts of media files that you can't normally play, some UI tweaks, an SSH server, and Boxee support.
(Update: Fire Core's site has a blurb mentioning Boxee as an "extended feature" for aTV Flash, but the problem is, the way their site's laid out doesn't make it clear if that's talking about the old version of aTV Flash or the new version. A commenter on Fire Core's blog indicates Boxee support is dependent upon XBMC Core being ported to the ARM architecture powering the new Apple TV, and it's unclear if the XBMC development team will do so or not. Consequently, It turns out the state of Boxee support isn't 100% clear for the new Apple TV.)
There is a big caveat though -- aTV Flash costs $50 for a license (which comes with one year of updates). Combined with the $100 cost of the Apple TV itself and you could almost have bought a Boxee Box, which would work without any modifications. Furthermore, it seems likely that other open source efforts will eventually bring most or all of these features to the Apple TV for free.
Click through for videos demonstrating the new UI offered by aTV Flash and the new last.fm streaming support that is being added to the latest version of Fire Core's software.