Some time a go I saw an interesting project called andLinux. andLinux is a complete Ubuntu Linux system running seamlessly in Windows 2000 based systems (2000, XP, 2003, Vista, 7; 32-bit versions only). The idea is that it runs almost all Linux applications without modification and you see the applications on your Windows screen like normal applications. Even cut&paste seems to work in most cases.
Earlier when you wanted to run Linux applications on Windows you needed to consider using a virtual machine (like vmWare player), Cygwin or coLinux. They all use different approaches to allow you to run Linux applications on your Windows PC.
andLinux actually uses coLinux (a port of the Linux kernel to Windows) as its core. Although this technology is a bit like running Linux in a virtual machine, coLinux differs itself by being more of a merger of Windows and the Linux kernel and not an emulated PC, making it more efficient.
andLinux uses Xming X server + virtual network interface driver to get Linux applications to show on your Windows desktop. The audio goes through PulseAudio sound server. I must admit that this andLinux worked as promised and was pretty easy to set up.
The biggest downside of it seems to be that it seemed to take noticeable amount of computer resources when it runs (memory was short on the system I tested it). Other things that make me worry what is the security of this whole system. The lacks of 64 bit Windows system support is also a minus at times when 64 bit OSes are coming more and more common.