“The Kaen is the oldest form of the free reed family, the great great grandaddy of the harmonica and accordion. This type of instrument goes back to at least 1100BC (the harmonica and accordion only go back to the 1830s).”
(read more about the kaen and hear a sample here)
This guy was playing on the street in front of the Shangri La; he played pretty well. The kaen makes such a beautiful sound on the city street. I dropped a 10 baht coin in his bowl and listened for a moment before walking by.