It's probably been brought up before, but the search function fails me, likely due to reign being a pretty normal world.
But, Greg Stolze's Reign. I heard about this recently. I am intrigued, and interested in seeing the Gaming Den rip it to shreds to see if it still sounds like good times after the dust clears. So have at it.
It's obscure, probably too obscure for there to be enough of a discussion of it here. I'm only passingly familiar with it: I know it uses the ORE mechanic and its rules for rulership interested me enough to, well, interest me, but I haven't read it in-depth or anything due to its size.