An open alternative is necessarily decentralised, standardized and extensible. Jabber/XMPP is a decentralized contact list with communication and authorization

An open alternative is necessarily decentralised, standardized and extensible. Jabber/XMPP is a decentralized contact list with communication and authorization protocols. It is easily extendable with XEP's. With a sleek web interface that anyone can host himself - this is an open alternative to facebook I imagine.