VirtualBox is a virtualization or emulation program that allows a virtual machine on your PC, with the ability to install Windows in another operating system, for example, if you have Windows XP operating system can run on virtually the Vista, or any Linux distribution, and also in reverse: from Linux run Windows, or other possible combinations between different operating systems.
The features and benefits of having a virtual machine are many, for example for those using Linux testing new distributions, or run a Windows program to which they are accustomed, but it does not support Linux. The same in reverse: for those users using Windows and begin their first steps in Linux can prove it, without having to create another partition, or install, or use GRUB.
VirtualBox is also useful for testing applications without running the risk of damaging the operating system, for example, suspected files that may contain viruses and is also useful for developers who need to test their applications on different operating systems.
Operating systems supported by VirtualBox are: DOS / Windows 3.x, Windows NT, Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows 7, Linux 2.4, Linux 2.6, OS / 2 Warp, and OpenBSD, among others; and now Mac OS X.
Virtual Box has competes with another program of the same characteristics as is the VmWare, but the former is lighter, completely free and also GNU (open source).
VirtualBox 4.2.0 is the latest version of this software, updated September 2012.
It is available to download a complete and detailed user guide from the official project site VirtualBox.
Free Download VirtualBox 4.2.0