Application virtualization is different than machine virtualization which virtualizes the machine on which an operating system (and applications) are installed. Machine virtualization provides an abstraction layer between the hardware and the OS that's running on top of it. It also allows managing and simultaneously operating multiple environments on a single machine. Application virtualization takes this concept and applies it to programs. The abstraction layer created by application virtualization lies between the operating system and the applications that run within it, allowing applications to be delivered dynamically as services that can be added or removed without installation. Microsoft purchased a company named Softricity a while ago and the  application virtualization product SoftGrid was forged from the algorithms created by both Softricity and Microsoft engineers. Marketing says: "Microsoft SoftGrid Application Virtualization provides the most extensive virtualization on the market. In addition to virtualizing application related Windows Services, it virtualizes per user, per application instance, key application comp