Guitar
A special electric folding travel guitar called the Foldaxe (briefly manufactured by Hoyer in 1977) was invented for Chet Atkins (in Atkins' book "Me and My Guitars") by inventor and guitarist Roger Field, featuring a built-in way to keep the string tension and tuning the same even when folded, and ready to play when unfolded. Atkins demonstrated his several times on US television, and also on The Today Show with Les Paul, who was with him as a guest.