I’m intrigued by the RocksterTek Porta-Guitar. It’s a collapsible guitar neck designed to let you practice chords anywhere. I imagine one could practice a subset of scales, too. This is one of those products that when I saw it made me instantly think, “Why hasn’t someone does this before?” And maybe they have, but I haven’t seen it. It’s a bit longer than 17-inches long when fully extended and just under 10-inches when collapsed. It can be restrung for lefties, and it comes with its own carrying back. I haven’t tested it yet, but it resonated with me when I first saw it. The RocksterTek Porta-Guitar is $39.95, and comes in black, pink, yellow, green, red, white, or sky blue.