php user management functionality

hey.... doing some basic research... has anyone found a seriously good user management script (preferably free) that can be incorporated within a web application. i'm looking for something that allows for the following functions: - user registration/login - admin function - group/team definition - email verification - database driven (mysql/postgres) - ability to grant user multiple rights/access levels - ability to check/deny by IP Address - session based function - page security - linux/apache/php we've seen a few, but nothing that really grabs us.... we're considering taking something like phpbb/gforge and just ripping the login/admin function out, although we'd prefer another approach.... but if we have to rip the functionality out of another app, has anybody seen an app (open source/free) that has a serious login/admin/user management function that we should look at... thanks bruce bedouglas@earthlink.net