Xbox Media Center (or XBMC) is an open source media program designed to run on an original Microsoft Xbox game console-- for an open source app designed on a "hostile" platform, it's actually got one of the better media center interfaces around (and it's easy to plug into-- you can even use your iPhone to control it remotely). And so the crew over there has recently been porting it back to work with Linux itself-- all of the Xbox Media Center, none of the actual Xbox.
If it's on Linux, it shouldn't be too hard to get it back running on OS X itself, right? At least that's what elan on the XBMC forums thought-- he hacked together a close-to-working XBMC port on Leopard. They haven't released it in any fully workable form yet (if you want to dive in as a developer, you can probably start here, and good luck, you're going to need it), but as a few people say, there's definitely a call for a terrific open source media center for OS X, because Front Row doesn't cut it for everyone.