The Open source edition of AtMail is provided as a lightweight and simple AJAX Webmail client. The commercial version of AtMail includes all the enhanced features such as Groupware, Calendaring, Advanced interface for IE/Firefox, POP3/maildir support, Mail-Server edition, Webadmin, Outlook Synchronization and more. For more details view the comparison chart for the two versions at http://atmail.org/compare.php