Final Version of Kolab Groupware 3.0 was released two weeks ago. It is a complete groupware suite that includes modules such as Mail, Contacts, Calendar and Tasks. It's strong advantage is support for synchronization of mobile devices.
Installation and configuration is easier than in other similar solutions. I used Debian Wheezy to setup test environment and encountered couple of minor problems but increasing debug level provided all needed information.
Documentation is available at docs.kolab.org.
I expected to see ownCloud integration but it is not there yet so I will wait and check this project from time to time as I plan in the future to eventually keep personal data on the private server.