OpenId

 OpenID  is an open community specification for Internet identity and Web authentication based on URLs/XRIs

It is a decentralized digital identity system, in which any user's online identity is given by URL (such as for a blog or a home page) or an XRI (eXtensible Resource Identifier), and can be verified by any server running the protocol (XRI v2.0 or later).

see: http://en.wikipedia.org/wiki/OpenID