Change a boxy style to a futuristic shape! Design your dream car with this Demonstration. The body consists of a single B-spline surface. You can modify the overall shape by changing the spline degree in each direction.
Of course, in reality, car bodies are designed much more elaborately. They usually consist of many rational spline surface patches, called NURBS (Non-Uniform Rational B-Splines). In Mathematica, SplineWeights can be used to make a rational B-spline surface.