We have just released ZK 6.5.2! Consisting of 18 new features and 80+ bug fixes including improved MVVM, improved theme customization & Portlet 2.0 support!
Release note: www.zkoss.org/product/zk/releasenote/6.5.2
New Features: http://books.zkoss.org/wiki/Small_Talks/2013/March/New_Features_of_ZK_6.5.2