For years I’ve been running my own CalDav/CardDav server to sync my Contacts, Calendars and Reminders across all my devices. I’ve been very happy with DAViCal, until recently, I had to switch to a simple vhost which doesn’t offer PostgreSQL and custom apache cfgs. So I did some research which other implementations may be useful, those are most promising ones:

Radicale (Python + Mysql)
http://radicale.org

Baïkal (PHP + Mysql)
based on SabreDav
http://baikal-server.com

SabreDav (PHP + Mysql)
DAV Framework,
https://code.google.com/p/sabredav

DAViCal (PHP + PostgreSQL)
Very complete, but not that easy to install.
http://www.davical.org

Other:
Apple CalendarServer: http://trac.calendarserver.org

See full list:
http://caldav.calconnect.org/implementations/servers.html