Came across this by accident.

I can just barely reach a tenth,
but I think a fifth would already be painful with this keyboard.

http://www.suzukimusic.com/education/pages/bigfoot.html

Wish my school could afford it. The kids would love it!

They are great fun to play on. But to get a good tune (at a resonable speed) you need several musicians, all playing only a few notes each (as if playing Hand bells!) Looks silly, but amusing