The Halifax Gibbet. I actually had a
history professor in a very reputable university not believe me when I mentioned its existence, or that of the Scottish Maiden. I had to bring him books to prove that the devices were real.
If you're into that sort of thing, there's a wonderful and fascinating book with a very inappropriate name: The Pleasures of the Torture Chamber. Mainly it's a very well-written history of torture and public execution, even though the title makes it sound like second-rate Sade.
http://www.amazon.com/Pleasures-Tort.../dp/1566197724