Prosody
From Organic Design wiki
Prosody is a light-weight, easy to configure, XMPP server. XMPP is an open and extensible Internet protocol used for communications, presence, identification, authentication etc. It's a big part of the Semantic Web movement which is all about achieving the functionality we need using open standards instead of specific applications.
Chatrooms
SSL
Todo: import script needed for LE certs, can use LE's hook