Thanks dtr,
I found some other uses as well:
The BMW Z4 is a 2-door, rear wheel drive sports car by the German automaker BMW.
or
The Z4 computer, designed by German engineer Konrad Zuse and built by his company Zuse KG, was delivered to ETH Zürich, Switzerland, in September 1950. It was the first computer in the world to be sold, beating the UK's Ferranti Mark I by five months and the UNIVAC I by ten months.