Oracle VM VirtualBox
VirtualBox is powerful Cross-platform Virtualization Software for x86-based systems.
"Cross-platform" means that it installs on Windows, Linux, Mac OS X and Solaris x86 computers.
And "Virtualization Software" means that you can create and run multiple Virtual Machines, running different operating systems, on the same computer at the same time. For example, you can run Windows and Linux on your Mac, run Linux and Solaris on your Windows PC, or run Windows on you Linux systems.
Oracle Introduces Oracle VM VirtualBox 4.1
Mac OS X running a Windows 7 VM