Roll cage
A newer form of rollover protection, pioneered on the Mercedes-Benz R129 in 1989, are hidden roll hoops.  When sensors detect the vehicle is about to roll over, the roll hoops quickly extend and lock in place.  Cars that have this kind of "deployable rollover protection" system include the Peugeot 307 CC, Volvo C70, Mercedes-Benz SL 500, and Jaguar XK.