If you’re familiar with what VMWare does (the creation of smaller virtual machines running concurrently on the same computer), then you’ll want to take a serious look at the latest release of the Xen Virtual Machine Monitor. What exactly is Xen, you ask?
Xen is a virtual machine monitor (VMM) for x86-compatible computers. Xen can securely execute multiple virtual machines, each running its own OS, on a single physical system with close-to-native performance.
If you have a few minutes, check out the project’s website and give Xen a try whenever you need to setup any sort of Virtual Machine, either for testing purposes or for some debugging.