Well there are many items on the list (which I don't have handy at the moment) but a few of them include:
-Generic audio encoding/decoding/processing frontend
-Complete audio file manipulation system including tagging, album/song management, renaming, organizing, playlist creation, processing, etc.
-Some sort of audio player, maybe with ability to read plugins from other players (we'll have to see about this)
-Various listening test tools
-Whatever else I forgot or other cool stuff that makes sense to add to the project
Basically all of this is going to attempted to be tied together with all of the different types of features people would want in the best programs from each categories, but all in one organized spot (kind of like this forum almost

). The entire thing will be programmed in Java and will utilize an XML based system for configuration (similar maybe to something like XUL in Mozilla) to provide a truly configurable and cross-platform system.
Of course, a lot of this is a ways off, but the abx listening tool is nearing a public beta (probably more like alpha

) quite rapidly, so that's a start.
There isn't going to be much activity related to all of this stuff for a good while yet though, just letting everyone know that now. Quite a bit of this is still in the idea/planning/experimental stage.
Nic, if you are interested in helping, and you can program in Java pretty well, you could always private message me and we could discuss the issue further.