I love Daniel Hulbert's Youtube channel, Circuits and Strings. He's always inventing new and radical instruments, especially ukuleles. His travel ukulele design is so compact and simple (as seen in the photo above and video below). I really think he should mass produce these suckers, but instead, he's freely given away the plans for any DIY'er to make their own. See the plans here.
Check out the travel uke in action: