Virtualbox

vbox_logo2_gradient.png Looking for some virtualization software? Look no further. Open source has you covered. Virtualbox runs on Windows, linux, and MacOSX. It also supports a variety of guest operating systems.
What’s nice is that even though it’s open source, it comes with a full SDK so you can write interfaces without having to mess with the innards of the beast. The virtual machine configurations are stored in XML so it makes porting virtual machines very easy. There are other features such as shared folders between hosts and guest operating systems, virtual USB controllers, support for Remote Desktop Protocol, and USB over RDP.
This is probably one of the better virtualization open source projects that is a bit easier for a user that doesn’t have a lot of commandline experience to actually understand and install.