OpenID eliminates the need for multiple usernames across different websites, simplifying your online experience. A user can choose the OpenID Provider that best meets his needs and that he trust. The user can keep his OpenID no matter which Provider he moves to. The OpenID technology is not proprietary and is completely free.
OpenID is growing quickly and becoming more popular as large organizations like AOL, Facebook, France Telecom, Google, LiveDoor, Microsoft, Mixi, MySpace, Novell, Sun, Telecom Italia, Yahoo!, etc. begin to accept and/or provide OpenIDs. Today, it is estimated that there are over one billion OpenID enabled user accounts with over 40,000 websites supporting OpenID for sign in.
OpenID was created in the summer of 2005 by an open source community (the father of OpenID is Brad Fitzpatrick) trying to solve a problem that was not easily solved by other existing identity technologies. As such, OpenID is not owned by anyone, nor should it be. Today, anyone can choose to be an OpenID user or an OpenID Provider for free without having to register or be approved by any organization.
The OpenID Foundation was formed to assist the open source model by providing a legal entity to be the steward for the community by providing needed infrastructure and generally helping to promote and support expanded adoption of OpenID.

Two directories are available to see where OpenID can be used to login :