Windows 3.1 onto a Nokia N95 handset. Marchin-PRV used DOSBox to emulate the x86-class processor on the Symbian handset in order to install Microsoft's 1992 OS. Totally useless, yes... and totally badazz.
Update: 3.1 too old-school for you? How about a little emulated Windows 95 action?
[Via OSnews, thanks yyy]