VirtualBox is a free virtual machine for Windows, Mac, Linux and Solaris. VirtualBox runs the disk images without the need for drive partitioning and difficult installation. The disk images can be placed on flash drives (thumb drives). This allows the disk image to be taken with the user and run on any computer that has VirtualBox installed.
VirtualBox can run different operating systems on the same computer. Many of the operating systems can be downloaded for free and legal. By downloading the VirtualBox disk image for an operating system, VirtualBox can run that operating system without having to install the operating system.
Virtual Box Disk Images Downloads
www.OSBoxes.org
www.VirtualBoxImages.com
www.VirtualBoxes.org
sourceforge.net/projects/virtualboximage/files (Not updated in years, but they may have something you are looking for)
VituralBox Free Download
www.VirtualBox.org