Cars companies all sort of work together.  The following lists of companies all have something to do with one another, ranging from putting different emblems on the same car (Ford Taurus and Mercury Sable) to collaborating (Nissan Z Coupe and Infiniti G35 Coupe) to owning shares of each other's companies. 

Ford, Lincoln, Mercury, Mazda, Volvo, Jaguar, Land Rover, Aston Martin
GM, Chevrolet, Buick, Pontiac, GMC, Saturn, Hummer, Saab, Cadillac
Dodge, Chrysler, Jeep, Mercedes-Benz
Nissan, Infiniti, Suzuki
Toyota, Lexus, Scion
Honda, Acura
Audi, Volkswagen, Lamborghini #travel