VirtualBox is a powerful x86 and AMD64/Intel64 virtualization 
product 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.

Presently, VirtualBox runs on Windows, Linux, Macintosh and OpenSolaris hosts and supports a large number of guest operating systems including but not limited to Windows
(NT 4.0, 2000, XP, Server 2003, Vista, Windows 7), DOS/Windows 3.x,
Linux (2.4 and 2.6), Solaris and OpenSolaris, and OpenBSD.

VirtualBox is being actively developed with frequent releases and has an
ever growing list of features, supported guest operating systems and
platforms it runs on. VirtualBox is a community effort backed by a
dedicated company: everyone is encouraged to contribute while Sun
ensures the product always meets professional quality criteria.