See http://www.cubrid.org/cluster. CUBRID Cluster is an open source clustered DBMS for high scalability including global schema, distributed partition and load balancing features. It is a spin-off project from CUBRID project and supported by NHN.
Moving to google code: http://yaci.googlecode.com Yet Another Cluster Installer) is a lightweight system tool used to reliably and quickly install large-scale (and small-scale) Linux clusters. It supports RedHat 7.3, 9 for i686, and RHEL3 and R
xCAT proper is now open source software! Please visit the xCAT site for more information on this incredible cluster administration tool: http://xcat.sourceforge.net/