phMyID - provide OpenID support to your site

phpMyID is a pair of PHP files that allow you to easily use your domain name for authentication to OpenID-supporting sites.

phpMyID is a single user (though, if you were so inclined, you could easily turn it into a multi-user setup) IdP, or "Identity Provider" for the OpenID framework. It's a single PHP script with minimal dependancies. You don't need a database, you don't need to make your filesystem writable, you don't need to download any libraries, and you don't need to recompile PHP.

Check it out here