Oracle VM VirtualBox is a free, open source, cross-platform application for creating, managing and running virtual machines (VMs). Virtual machines are computers whose hardware components are emulated by the host computer. Here is a picture of VirtualBox in action:
Oracle VirtualBox enables you to set up one or more virtual machines (VMs) on a single physical machine, and use them simultaneously, along with the actual machine. Each virtual machine can execute its own operating system, including versions of Microsoft Windows, Linux, BSD, and MS-DOS. You can install and run as many virtual machines as you like – the only practical limits are disk space and memory.