We used to have one of these when we were kids (although, I don't think we called it a Zither.) I spotted it on Etsy a few days ago from seller HeartandHomeLC and immediately bookmarked it. I would love to buy one again!
I think this is a great way to get kids interested in music and playing instruments. It's a simple independent activity. (Note: the seller recommends this item for children older than age 4.)