Baikal with Nginx and https
If you want to have your calendar- and contact-data synchronized and don't want to give it away to third parties, it is possible with very simple means to synchronize it at home on your own server. The flagship in this direction is OwnCloud, which also provides CalDAV and CardDAV for synchronization. However, I had always had problems with the synchronization, and so I wanted to give Baikal a try.
Baikal is a PHP written, small and robust server to synchronize calendar and contact data using CalDAV and CardDAV.