AfterLogic WebMail Lite PHP is a free AJAX webmail application. Users can receive, view, manage, compose, and send email through web interface (IMAP and SMTP supported). Source code included.60 weekly downloads
This plugin enables Roundcube to access the addressbook of the user in a Kolab-Envoirenment. So you can keep your addresses in Roundcube in sync with the address in your other (Kolab-enabled) PIM-clients (like Thunderbird, Outlook and so on).