OpenID is a decentralized identity system, but one that's actually
decentralized and doesn't entirely crumble if one company turns evil
or goes out of business.

An OpenID identity is just a URL. You can have multiple identities in
the same way you can have multiple URLs. All OpenID does is provide a
way to prove that you own a URL (identity). 

Anybody can run their own site using OpenID, and anybody can be an
OpenID server, and they all work with each other without having to
register with or pay anybody to "get started". An owner of a URL can
pick which OpenID server to use.

WWW: http://www.openid.net