Just wanted to clarify a couple of things. The Songbird SVN has been down for some months now, but they did put up the link mentioned in the comments above fairly recently.
As for Nightingale, we're still staying around even though we're not perfect yet, we have a handfull of devs still owrking on things - right now we're working or way to using a modern xulrunner instead of 1.9, which is what Songbird and Nightingale have used up until now. We're also going to ask POTI if we could get the source code to their closed source addons, such as MTP and DLNA support, and for the source to their addons platform with it's database, and the source to the mobile versions. We're game to maintain and improve upon all they offered, it's just going to be interesting to see how they respond.