The Guitaro is an autoharp that is designed to be played standing up, like a guitar. This one is a pretty good specimen, and was purchased on eBay.
According to Wikipedia, it was manufactured by Oscar Schmidt-International in the mid-1960’s through the early 70’s. It has 24 strings, but the tuning is lower than a standard autoharp, because of the string length.
Here is a video of Sara Carter playing one on TV
Mother Maybelle & Sara Carter - While The Band Is Playing Dixie
In combination with my DeArmond autoharp pickup, you can do some pretty cool things with this - pedals, amps, distortion etc.
Microtonal music would be facilitated with a non-fretted instrument like this. So some just intonation, or other microtonal scale could be easily setup.