VMware have been making their virtual machine technology for some time, and I've been a long time fan (and beta tester) of the product since the original version.

Now VMware are making their VMware player available for free. Basically a run-only version of the VMware software, it means that you can run a virtual machine, assuming, of course, that a virtual machine already exists for you to use. From the official blurb:

VMware Player is free software that enables PC users to easily run any virtual machine on a Windows or Linux PC. VMware Player runs virtual machines created by VMware Workstation, GSX Server or ESX Server and also supports Microsoft virtual machines and Symantec LiveState Recovery disk formats.