Sun xVM VirtualBox downloads are now available for most OS's including GNU/Linux, Mac OSX, Solaris and Windoz !
VirtualBox binaries are available for download under the PUEL (Personal Use and Evaluation License). This allows anyone to download and use the product free of charge in compliance with those terms.
For organizations that want to deploy across the business, Sun offers Sun xVM VirtualBox Enterprise Subscriptions
which includes a Sun Software License Agreement and Premium Service Plan.
Sun xVM OpenVirtualBox
VirtualBox source code is freely available and licensed under GPL2 as the Open Source Edition.