I think it's possible to make a 3 position snap switch using a mechanism where the contact would get stuck in the middle until the spring's angle changes far enough that it can move all the way to one side. I think 3 position mercury switches would be possible using a bent mercury capsule so the mercury could rest in either side as well  as the middle. I also think dimming mercury switches would be possible using a bent mercury capsule and bent carbon rods as the contacts.