Laravel Impersonate is a plugin to authenticate as your users
Admidio is a free open source user management system for websites
Login with Multiple Hierarchies of User and Members!
Manage your organization online
Award-winning lightweight Open Source Content Management System (CMS)
Sita Access Manager (SAM) is php based Login System.
Secure login system for php frameworks, applications ansd sites
Free and Open Source Web Sites Builder
A simple web login system written in PHP and using MySQL database.
Simple user login management in php with sessions.