caldav, cardav
http://sabre.io/baikal/install
DAViCal is a server for calendar sharing. It is an implementation of the CalDAV protocol which is designed for storing calendaring resources (in iCalendar format) on a remote shared server.
https://www.davical.org
sabre/dav is the most popular WebDAV framework for PHP. Use it to create WebDAV, CalDAV and CardDAV servers.
http://sabre.io/dav