I missed this one when I visited the Microcar Museum:
It is a prototype of a Jurisch Motoplan. This is the only one known to exist, and is quite a vehicle.
You can tell from the picture that it uses a Heinkel engine. There’s more Heinkel underneath and inside:
This looks like a Heinkel scooter gas tank and exhaust, possibly from a 103-A0.
Inside is a Kabine shifter mechanism from a rod-change Heinkel. The car doesn’t have a steering wheel. You steer with two levers on either side of the seat. I bet that takes getting used to.
You can learn more about the car from http://www.germanmotorcycles.cl (which is also the source of some of these pictures).
The car is part of the Microcar Auction in February. Estimated price for this one of a kind vehicle is $50-$75,000!.