Lol, on a default Windows install you can have 5 different MS apps with different size borders, title bars and controls. Even two different control panels, each with haphazard conflicting UI elements within them. I think it's kind of insulting to put "open source UI" in 4th position because I see a lot more effort and thought going into it that in many proprietary apps (jeesus just look at the average app on a mobile device)