EGroupware is a multi-user, web-based groupware suite. Currently available modules include: email, addressbook, calendar, infolog (notes, to-do's, phone calls), content management, wiki, project management, tracker, timesheet, knowledge base, CalDAV/CardDAV
Very good groupware by the set of features. Unfortunately I couldn't get the mail module to work in version 14.1 (with a standard setup and installing packages from the source list), always ending up with "emailadmin_imapbase::openConnection (841) ->open connection for Server with profileID:8 failed! Tried to access unknown attribute 'capability'!". That's mission-critical but maybe they manage to fix this issue. I am furthermore missing SyncML which was abandonned after version 1.8. However it is one of the very few solutions that supports CalDAV and CardDAV. One should be prepared to spend quite a time for the configuration. There is no manual, just a (quite minimalistic) setup tutorial. I don't know whether paying customers get some documentation.