The PostNuke CMS was a fork from the earlier PHP-Nuke. Both of these are still active and widely used, but the PostNuke creators have split off again to do a major (and much needed) rewrite of the system, now called Xaraya.
This continual splitting process is either one of the greatest strengths or greatest weaknesses of Open Source software, depending on your point of view. Either way, Xaraya looks much better under the skin than its predecessors, and is starting to gather accolades, but is badly in need of some really nice documentation like Typo3.