GUEST with no name, I agree with Bill D. There are several weird and wonderful instruments that were invented and sold at the same time as the Autoharp, but the Autoharp seems to be the only one that really caught on.
The Guitar zither has chords to the left and single strings to the right (no chord bars) and has a shape similar to the Autoharp.
The mandolin zither is similar to the guitar zither, but has two string courses.
The ukelin works similar to the last two zithers, in that you have chords played by one hand and melody with the other, but on the ukelin you play the chords with your thumb or a pick and the melody is bowed.
There were other similar, but different instruments that you'll see at garage sales, pawn shops and flea markets. Not many folks actually learn to play them and they end up hanging on a wall or sitting in an attic.
There is a concert zither which is still used, usually in Europe, which has a fretted fingerboard on the left side and single strings on the right, but I doubt this is the one you've found.