What do you get if you cross an accordion with a harmonica?
One person who did just that was Ernst Zacharias and in so doing the Hohner Harmonetta was born.
They're pretty unusual but I did see 3 on Ebay during November and December last year - one of which sold for $750, and another sold for 370 Euros. So they're quite valuable too.
Judging from the videos on YouTube they aren't easy to play solos on, but this guy can do it.
More usually they're used to provide the rhythm in harmonica bands, a prime example being Svang.