Let your users to use their username and password from other Drupal sites.
It IS the old "Drupal" module which just left core.
- Let drupal.org users to login into your site using their old login/password.
- Alternative for OpenID
- Multi site environment: split your site functionalities into many sites but use a central user database. Like drupal.org and groups.drupal.org
Since its yet a simple port from Drupal 5's "Drupal" module, it yet have some important issues (present on the old module too):
- No user data is get from the server (email for example). see http://drupal.org/node/61738
- Password is sent without cryptography, and is therefore insecure. See http://drupal.org/node/93048
- The password insertion is done in the site's domain, so they might (but not by this module) capture your password
Use of this module is advised as a compatibility replacement for Drupal 5's distributed authentication, but migration to OpenID is suggested instead.