I have started something: http://code.google.com/p/fpbitcoin/ but Its running on low piority at the moment. I hack on it a few hours every few days. I'm doing this (mostly on my own) as an attempt to (a) learn and understand every little detail of the bitcoin protocol and (b) to document for me (and others) what I have found.

If everything succeeds then the end result will be a lightweight cross platform bitcoin client (a non-gui unit implementing the bitcoin protocol and a rich graphical client to manage a wallet) that does not suffer from the many problems of the "official" client. But this might take some time until its usable since I'm only working part time on it and I want to do most of it myself (for the learning effect).