Though not a Celtic musical instrument, the Strumstick, a kind of simplified guitar, could be used to play almost any kind of music. The instrument was designed by Bob McNally, famous for his collaboration with Martin Guitars in the development of the Backpacker Travel Guitar. The Strumstick was invented for anyone who doesn't know music or play any instruments, for children, and for adults who have suffered setbacks in their attempts to learn more complicated instruments.
The motivation for creating the Strumstick was that beginning musicians need to feel some sense of achievement and progress right from the start, or they may abandon a new instrument entirely. The Strumstick breeds success right away. Since there are no wrong notes, anything you play on it sounds good. To begin, you squeeze the first string with one finger, and strum all three strings with a pick; the other two strings produce a background chord automatically. You don't need talent or experience, and your tin ear won't hold you back. It's very easy, and beginners get results immediately, making the Strumstick the ideal first instrument for children (supervision recommended for ages 3-5). The only requirement is a desire to have fun!