Do you want to run Windows on your Mac but don't want to buy Parallels or VMWare Fusion? There is a free program called VirtualBox that is Open Source that reportedly does the same thing. According to their Web site:
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the GNU General Public License (GPL). See "About VirtualBox" for an introduction.
It is on my list of things to try out. As companies lay off talented programmers expected that pool of talent to find expression supporting Open Source projects like this.