Source: http://en.wikipedia.org/wiki/Mbira.htm
The kalimba, known by far too many names in different cultures to mention here, may be regarded as a handheld xylophone. The bars are of course much smaller, resulting in a much higher pitch, while the instrument typically has a single soundbox for all the bars.The bars are also fixed on one end, leaving the other end to vibrate freely. In ancient times perhaps sticks were used as bars, but since metal smelting was invented, the bars have been made of metal. Instead of striking the bars with a mallet, the fingers are used.
Source: http://en.wikipedia.org/wiki/Mbira.htm
http://www.youtube.com/watch?v=tg24k7tzIc0