Every game needs rules for Vehicles.
Dream Pod 9 has some nice rules for creating vehicles, though they are math intensive at times. An independent game called Journeyman also had some nice rules for creating starships, but the best starship rules I've ever read were in the Traveller supplement High Guard. As I said, Traveller had some nice rules for creating starships, and they eventually came out with some rules for creating vehicles, like cars and grav tanks. But these rules were needlessly complicated, and didn't have the spark of the starship or character creation rules. Gurps has some of the finest character creation rules on the planet.