Somebody pointed me to this wonderful mudclient and after seeing some screenshots I gave it a testrun. The first thought that crossed my mind was 'Is this Open Source?' and 'Is there some CVS or SVN repository available for developpers like myself?
Seeing the background a bit of the development of the client I am afraid that the answer to both would be no, but it never hurts to ask, does it?

Sure doesn't hurt to ask, but yes you've reached the right conclusion. Sadly, Batclient is not Open Source, thus no repository is available for your perusal.

Balanced Alternative Techniques ry ("B.A.T. ry") has been heavily funding the development of this Official (and unique) game client for BatMUD.

However, if you're interested in doing Your own plugins, scripts or triggers for Batclient, you're free to do so, see http://www.bat.org/client-plugins