“The rationale for Universal is web applications such as Phorum, phpBB, WebCalendar, PostNuke, Xaraya, Drupal are unable cooperate because there is no data sharing. Universal is an attempt at bridging these islands of data by providing means for PHP applications written by different people to work better together. As a PHP developer, you can help make PHP web applications interoperate by implementing a shared sign-on mechanism based on the specs described here.”
http://php.weblogs.com/universal