SOGo

SOGo is a free and open source groupware server for calendars, address books, and mail. It is built for businesses and communities that need shared collaboration tools in one web-based system, with a focus on scalability and open standards.

A rich AJAX web interface covers calendaring, address book management, and webmail, alongside resource sharing and permission handling. Native clients connect through standard protocols including CalDAV, CardDAV, GroupDAV, and Microsoft ActiveSync, so iPhone, Android, and Windows Phone devices can sync mail, contacts, events, and tasks. Microsoft Outlook is supported through the Outlook CalDav Synchronizer.

SOGo is developed by the community together with Alinto and is released under the GNU GPL and LGPL v2 and above. It is a server-side groupware product you deploy yourself rather than a hosted service.