Xen is a hypervisor based virtualization technology originating at the University of Cambridge, nowadays developed largely by the company [http://www.xensource.com/ XenSource]. Xen introduced the concept of paravirtualization, which allows for extremely high performance virtualization provided that the guest virtual machine runs a modified operating system kernel.
Xen also supports full virtualization (running unmodified operating systems) on processors with Intel VT or AMD-V technology.
Xen is available in many Linux distributions, however ["lhype"] and ["KVM"] appear to be making more progress at getting merged into the upstream kernel...
How to use [:XenWifiNetwork:Xen with a mobile network], for example on a laptop.
[https://virt.108.redhat.com/articles/2007/01/15/xen-guest-installation.pdf Lab 1: Xen Guest Installation (PDF)] - Learn how to install RHEL3, RHEL4 and RHEL5 beta 2 and WinXP on Xen
[https://virt.108.redhat.com/articles/2007/01/15/xen-live-migration.pdf Lab 2: Live Migration (PDF)] - Want to move an executing workload from one node to another? Here's how.
[https://virt.108.redhat.com/docs/ETXenVirtQuickRef.pdf Xen virtualization commands, at a glance. (PDF)]
[http://jailtime.org/ Jailtime] a site with many different Xen guest images.