this flat-folding 'thinbike' was custom built to fit in a hallway without taking up any space. the best part about it is the 'speedlifter' system, which allows the handlebars the turn 90 degrees and stay out of the way.
i have something very similar to this on a shopper bike i have, but it is a lot more primitive. i didn't even realise these existed for mountain and road bikes! i had seen the ninety bike last year, but am now very intrigued to try out a speedlifter for myself.