Not a real “FAQ” but we should have a place where all CalDAV/CardDAV clients are connected.
CalDAV clients:
http://caldav.calconnect.org/implementations/clients.html
CardDAV clients:
http://carddav.calconnect.org/implementations/clients.html
Sync clients:
https://forum.owncloud.org/viewtopic.php?f=14&t=2694