BMW Isetta

The Isetta is an Italian-designed microcar built under licence in a number of different countries, including Spain, Belgium,France, Brazil, Germany, and the United Kingdom. Produced in the post-World War II years, a time when cheap short-distance transportation was most needed, it became one of the most successful and influential city cars ever created. Because of its egg shape and bubble-like windows, it became known as a bubble car, a name later given to other similar vehicles.

The BMW Isetta was in 1955 the world’s first mass-production 3-Litres/100km car. It was the top-selling single-cylinder car in the world, with 161,728 units sold.[wiki]