There Are No Free Hypervisors – Citrix Xen, Microsoft Hyper-V, and VMware ESXi will all Cost you in the End - Virtualization News Resources

VMware has just made VMware ESXi “free”. Citrix makes a big deal out of the fact that its Xen hypervisor is “free”. Microsoft’s Hyper-V is included in Windows Server 2008, so it is “free”. However, none of these products is really free; you will pay for all of them in various ways.