VirtualBox Ubuntu 10.04 Lucid Lynx Repository

Oracle VM VirtualBox is an x86 virtualization software package, originally created by German software company innotek GmbH, purchased by Sun Microsystems, and now developed by Oracle Corporation as part of its family of virtualization products. It is installed on an existing host operating system; within this application, additional guest operating systems, each known as a Guest OS, can be loaded and run, each with its own virtual environment. In plain English: you can basically install Linux as a guest OS inside Windows or the other way around, and so on without affecting the currently running OS.