Zundapp, an established motorcycle company, produced this remarkable microcar from 1956-1958. 

Zundapp JanusZundapp Janus

Hoffmann [DE]1949-1954

Hoffmann manufactured bicycles before venturing out into the world of motorcycles and microcars. The Auto-Kabine 250 was based on the Isetta, but the design was adapted somewhat (side doors) as they were unable to acquire an official licence from ISO. BMW (who did have a licence to make Isettas) successfully sued Hoffmann, who had to cease production after just over 100 vehicles had been sold.

1955 Hoffmann: Auto-Kabine 250

Heinkel [DE] 1955-1958

Opperman GB 1956-1959

The Unicar was a 2-4 seater microcar constructed from fibreglass. It had a rear-mounted 2-stroke 2-cylinder engine of just 225 cc or 328 cc.The car was also available in kit form. This miniature GT model, called the Stirling, made its debut at the 1958 London Motor Show. Engine size had grown to 424 cc. Very few were sold.

1958 Stirling

Bond (UK)

Bond produced their first 3-wheeler in 1948/1949. The first models were fitted with Villiers 2-stroke motorcycle engines. In 1965 the two-strokes were replaced by Hillman Imp units, mounted in the rear. In 1970 Bond introduced the Bond Bug, an entirely new design by Tm Karen,featuring a hinged roof instead of doors. The engine was a 4-cylinder 701 cc unit that delivered 29 hp at 5000 rpm.
Bond also produced some nice-looking sports cars between 1963 and 1971 called the Bond Equipe.