Free Mac and PC Virtualization Software.
Virtualbox is a new virtualization offering like VMWare for desktops on PCs, Macs and Linux.
Fully open source, and apparently quite Mac friendly.
Not perfect, but you can’t argue with free. Myself however I will probably stick with VMWare Fusion, a great afforadable product.
Get it here: http://www.virtualbox.org/wiki/Downloads
