VMWare vSphere 4

Read more about the new upcomming ESX3.5 replacement

http://www.vmware.com/products/vsphere/

VMware vSphere is the industry’s first cloud operating system, transforming IT infrastructures into a private cloud—a collection of internal clouds federated on-demand to external clouds—delivering IT infrastructure as an easily accessible service. Enable the next generation of flexible, reliable IT services with the efficiency and low cost of cloud computing—featuring uncompromising control over service levels.