Apache Vysper - A modular, full featured XMPP (Jabber) server

Apache Vysper aims to be a modular, full featured XMPP (Jabber) server. Vysper is implemented in Java. There are already some larger XEPs as modules available, most notably Multi User Chat (XEP0045), Publish/Subscribe (XEP0060) and BOSH (XEP0124, XEP0206)