I found a great post on how to get a working PaaS cloud using only open source technologies. It goes trough OpenShift, Katello, Aeolus and oVirt.

it's always fun to see what technology can do, and if we don't tinker we'll never drive vision to reality

See it by yourself: http://allthingsopen.com/2012/10/16/open-hybrid-paas/

Red Hat Enterprise Virtualization going open source as oVirt [relaunched]. There will be a workshop in November, open to all who want to use, get involved or learn about the comprehensive open virtualization management platform. The sessions will cover the technical projects details, governance, getting involved, usage and much more.

Full GIT repos (source), site, forums will be launched at the event!