OpenID is a free and easy way to manage your identity across different websites. Instead of having lots of different usernames and passwords for lots of different sites, OpenID acts as your single point to verify that you're you, so you can join or login to the website you're visiting.
It is very secure, you set the level of information you wish to share with leaguist and it does have the backing of Google, IBM, Microsoft, VeriSign, and Yahoo!
If you'd like to learn more about other websites using OpenID, have a look at myOpenID Site Directory or The OpenID Directory.