Windows Phone, eat your heart out. Android is now capable of virtualizing a full and up-to-date Windows desktop operating system. Well, one phone is at least, and it's probably not one you would have guessed: the ASUS ZenFone 2. XDA-Developers forum member ycavan managed to get Windows 7 running on his phone using a variety of custom tools, some impressive technical skill, and quite a lot of patience. Check it out in the video below:
To be clear, this is Windows 7, virtualized, running on a local virtual machine client accessed via the aSPICE KVM client for control. Windows is not being emulated (it's been done with older versions). The virtual machine is slow, but surprisingly usable. All of this is made possible thanks to the x86 architecture of the ZenFone 2's Intel Atom processor. I doubt you could get Windows 7 running at acceptable speeds, using a virtual machine or any other method, on even the latest ARM-based hardware.
If you'd like to recreate this feat, ycavan has posted exhaustive instructions on XDA. You'll need to unlock the bootloader on your phone and install a custom kernel, among other things, and of course you'll need a copy of Windows 7 itself. Good luck - this is not for the faint of heart.