Via: flickr - Fine Cars
Einspurauto - one track car (Winkler / Mauser)
This vehicle was developed in 1920-1921 by the German engineer Gustav Winkler, and was built by the Mauser fire-arms factory. Mauser factories who, after WW1, weren't allowed to produce fire-arms anymore.
The Einspurauto's had a body, a door and stabilizing side wheels on both sides. They were powered by water cooled 510 - and 576cc singles. This particular construction didn't sell very well and in 1926 Mauser stopped manufacturing them. Winkler then made the machine a few years himself.
Via: flickr - technikmuseum