Eucalyptus is an open-source software platform that implements IaaS-style cloud computing using the existing Linux-based infrastructure found in the modern data center. It is interface compatible with Amazon's AWS making it possible to move workloads between AWS and the data center without modifying the code that implements them. Eucalyptus also works with most of the currently available Linux distributions including Ubuntu, Red Hat Enterprise Linux (RHEL), CentOS, SUSE Linux Enterprise Server (SLES), openSUSE, Debian and Fedora. Similarly, Eucalyptus can use a variety of virtualization technologies including VMware, Xen, and KVM to implement the cloud abstractions it supports.
Helpful Links:
http://www.eucalyptus.com/products/overview
http://open.eucalyptus.com/wiki/EucalyptusUserGuide_v1.6
http://open.eucalyptus.com/wiki/eucalyptus-administrators-guide-16