OpenEJB - an open-source ejb container from the author of the o'reilly ejb book . Very much under construction: not really useful at the moment but a great opportunity to find out how an EJB container really works. http://openejb.exolab.org/
JOnAS Open Application Server for EJB, looks like it was written by a research group inside Groupe Bull and now it's a spin-off called Evidian. http://www.evidian.com/jonas/index.htm