OpenID Provider helps you use your Web site as a source of Open IDs. Using example.com as your Web site and 3 as your internal user id, you can log into an Open ID site using example.com/user/3.
The module is at http://drupal.org/project/openid_provider.
XRDS Simple: http://drupal.org/project/xrds_simple
Your name is Adrian. Your user page is example.com/user/76467/identity. You could use Path or another module to translate example.com/user/76467/identity to example.com/user/adrian or example.com/adrian and your Open ID login would be easier to remember. You could use an Apache redirect in the Apache .conf file or a .htaccess file to translate adrian.example.com to example.com/user/adrian and your login becomes even easier.
If your name was Adrian Tjupurru (you would be a very entertaining musician) and you registered http://tjupurru.com (done), you could set your site so you can log into Open ID sites as adrian.tjupurru.com.