Strange accordion-piano instrument?

I saw a neat instrument, don't know what it is. A reed & air instrument, very similar to an accordion and about the same size. It was on the ground, keyboard facing the player & played like a piano with one hand, and a bellows on top was fanned back and forth (toward and yon the player) with the other hand. It was with some religious people (don't know what kind), but I think I've seen that sect with it more than once in different parts of the country. Anybody know what it is?