Why is the Audi A2 considered a pioneer in alternative fuel vehicles?

I've heard that the Audi A2 was ahead of its time in terms of alternative fuel usage. Can you explain what made this car a pioneer in that area and how it has influenced future vehicle technology?

The Audi A2 was the first production car to use an aluminum space frame, which was not only lighter and stronger, but also more environmentally friendly compared to traditional steel frames.

Additionally, the A2 was available with a groundbreaking natural gas engine, reducing emissions and promoting the use of alternative fuels in everyday vehicles.