I saw Wordpress was shared here, so I wanna share #TYPO3
The current Version is 6.0.
There is also a PHP Framwork called #FLOW
and a new early released version of the new CMS #NEOS
TYPO3 is an open source enterprise CMS.
Some of the code is a bit old, but there is a nice backport of the PHP Framework FLOW available as an Extension.
You can either use this cms as a simple cms, or to handle multilingual sited, with multiple domains and extend it for your needs with a nice framework. There are also many extensions available in the official TER (=TYPO3 Extension repository).
There is also a Community available here on G+: https://plus.google.com/communities/104410053692531620800
Of course there is a wiki, docs, irc, mailinglist, ...