Image courtesty of these guys! http://moto.zombdrive.com/sommer/sommer-diesel-462/ 
Image courtesty of these guys! http://moto.zombdrive.com/sommer/sommer-diesel-462/ 

Just look at this thing! Comes in two sizes: The 462 Hatz diesel shown, and the 516. Straight out of the Sommer motorcycle company in Austria.

Link here (especially useful for you German speaking folks)

http://www.motorradmanufaktur.de/index.php