There have been two X-body automobile platforms from General Motors. All X-bodies were small entry-level sedans.
Rear wheel drive
The rear wheel drive X-body underpinned the Chevrolet Nova and similar cars of the 1970s. It was also the basis for the Cadillac Seville's K platform. The wheelbase was 111 in and many components were shared with the contemporary F platform.
Applications:
Front wheel drive
The front wheel drive X-body was used for compact cars from 1980 to 1985. The X-body program was widely considered a failure at the time, but the derivative FWD GM A platform, which was introduced in 1982, continued for over a decade. Interestingly, only the Skylark name was carried over to the next generation of GM compact cars: the N-body.
Vehicles using the X-body include: