Kalimba (factory-made African "thumb piano"):
- small,
- cheap,
- logical (you can "see" high & low),
- you can sing with it,
- the tines next to each other are in harmony,
- it's hard to make it sound bad,
- tends to stay in tune,
- sturdy,
- relatively rare,
- has a great sound, and
- can be tuned to different scales.