from VirtualBox News page:
Jan 15, 2007. InnoTek today released VirtualBox Open Source Edition (OSE), marking an important milestone in the development of PC virtualization software. VirtualBox OSE is the first professional PC virtualization solution released as open source under the GNU General Public License (GPL). With VirtualBox, customers get the most versatile virtualization product on the market, both for enterprise and individual use. VirtualBox' open source license allows everyone to contribute to the development of the product and customize it to suit individual needs. Backed by Europe's largest team of virtualization experts, VirtualBox continues to be developed and supported.