Don't you think the JBoss website would be a good place to find out?
Quote from the website:
* JBoss was started in 1999 as an open source EJB container. * JBoss 2.x was a full J2EE 1.2 based server. * JBoss 3.x is our current J2EE 1.3 production series. * JBoss 4.x is our current J2EE 1.4 production version. * JBoss 5.x is our current developer version.