Though there are some free virtualization tools available, most have limitations. VirtualBox is a free open-source virtualization tool powerful enough for enterprise systems yet easy enough for home users. It runs in Windows editions 95 to 7, Mac OS X, Solaris, and Linux, and it supports a wide range of guest operating systems, including MS-DOS, early versions of Windows, and OpenBSD.
VirtualBox's wizard-based interface simplifies the creation and management of virtual machines (VMs). The tabbed main display is paired with a side panel listing all existing VMs. Control icons labeled New, Settings, Start, and Discard handle all functions, and tabs for Details, Snapshot, and Description display information about any selected VM. We clicked New to create a new VM to install Ubuntu, the free Linux-based OS, within Windows 7 to test VirtualBox's ability to host multiple operating systems without making drastic changes. The wizard let us select the operating system (Linux) and version (Ubuntu) we planned to install during the creation, as well as specify the amount of RAM to allocate for the new VM. Next we created a new virtual hard disk, though you can select an existing bootable disk image. You can choose to create either a fixed or dynamically expanding disk; we chose the latter. If you need more RAM or disk space, the Settings icon accesses these options as well as other settings like audio, USB, and serial ports. When everything was ready, we clicked Start, followed the First Run Wizard, and created a custom-configured VM ready to host our new OS. Surprisingly, VirtualBox even had a wizard for that. While you're using your VM, you can always exit back to the host system instantly with a specified keystroke.
VirtualBox was developed by Innotek, which is now part of Oracle, and VirtualBox is part of Oracle's extensive support system. Add the advantages of open-source development and the fact that's its totally free to both enterprise-level developers and home users, and it amounts to a strong recommendation.