If a system is going to be used, nWOD would probobly run it best of any non indy system, although RISUS might also work pretty well. nWOD would cover making fairly low powered characters and provide mechanical incentives for doing stupid things, while RISUS would effectively portray the difference between robot and human power levels, and also provide a mechanism for the indestructability of the robot.
As for setting, you could do a pretty interesting future setting in witch the robot is the warden of a futuristic prison, but has gone berserk, forcing the prisoners to battle the thing with improvised weapons and good old fashioned human sacrifice, which is of course decided in a completely democratic manner. :)
As the robot tears through more and more security barriers in the prison, the prisoners have a chance to escape; but what if the robot going berserk was not an accedent, but a deliberate test of a new military weapons system, for that matter, why are there so many nanorepair kits, assault rifles, and plasma cannons lying around the prison in places they shouldn't be? And why, exactly, has the robot been smashing through every wall except the outer wall?
Sometimes, when you look out the windows, you see shadows outside the prison, are they black ops government spooks? Or has the rise of the machines finally come?