Open source push technology.

Z-Push is an open-source application to synchronize ActiveSync compatible devices such as mobile phones, tablets and Outlook 2013 and above. With a history of over 9 years of successful synchronization with multiple backends Z-Push is the leading open source push synchronization.

• Z-Push @ GitHub.

Open Source Groupware.
SOGo is a fully supported and trusted groupware server with a focus on scalability and open standards. SOGo is released under the GNU GPL/LGPL v2 and above.
SOGo provides a rich AJAX-based Web interface and supports multiple native clients through the use of standard protocols such as CalDAV, CardDAV and GroupDAV, as well as Microsoft ActiveSync.