In the past few years, we have covered plenty of apps that let you compose music on your phone. The Skwitch is a cool little music accessory that turns your iPhone into a musical instrument. It lets you play the songs you know or compose new ones. The Skwitch clips onto your phone and doesn’t require a separate battery to work.
You can use this device with GarageBand and other music apps. The Skwitch has a highly tactile sensor to respond to your slightest touch. More info is available here.