Open Source Self Service Portals for VMware, XenServer, KVM and other virtual servers:
Open Eucalyptus http://www.eucalyptus.com
Cloud Stack http://www.cloud.com
Convirture http://www.convirture.com/ (Supports VMware)
Self service cloud software is cool, but you’ll also need a hypervisor. I highly recommend you take a look at these virtual machine program alternatives to see if there is one that will work for your existing hardware environment.
All links are Free or Open Source Cloud Portal Software.*