There are commercial products like VMWARE available to support virtualization. But there are various Open Source tools available that give similar features to the commercial products.Virtualization has been like a revolution and has reduced the cost of the company greatly and virtualization is a part of cloud technology, that makes it a technology to watch out for.
KVM stands for kernel-based Virtual Machine,though not so widely used but now has gained some users.KVM can run both on Linux and Windows.Red Hat’s virtualization server is now based on KVM Hypervisor.
Xen is the hypervisor that ships in with Linux.It supports paravirtualiztion and hardware assisted virtualization. Xen hypervisor operates as the lowest and most privileged layer.Above which there comes other guest operating systems which is scheduled by the Hypervisor across various CPU’s .The first Operating system ie. Dom0 boots automatically at the start of the hypervisor and it gets special privileges and can access all physical hardware.It further helps in managing of other Guest Operating systems.Xen can be found at https://www.xen.org
VirtualBox is tool which was developed by a German company Innotek which was later acquired by Sun Microsystems, which was again later acquired by Oracle. VirtualBox is one of the most widely used virtualization software and runs on Windows, Linux, Solaris and Mac OS X and can support all those operating systems as guests. It supports hardware virtualization also.VirtualBox can be found out at http://www.virtualbox.org