OpenID is a way to authenticate yourself to various web services as the owner of a particular URL. Instead of giving a username and password to a login form, you just give it your URL. You're then directed to your "identity provider" to log in, and when it authenticates you, you go back to the site you were orignally trying to get into.
Now instead of getting an OpenID from third-party provider, you can use phpMyID that let you use your own domain name for authentication to OpenID-supporting sites like Sourceforge, Skitch, and Technorati without giving control to a third party.
More info: phpMyID