What cars are compatible with a 2000 Saturn LS1 motor?

There's no such thing as a "2000 Saturn LS1 motor." The LS1 engine is a General Motors engine, notably used in Chevrolet Camaros, Corvettes, and other GM vehicles, starting in 1997. Saturn, at that time, used its own completely different engine families. Therefore, no Saturn is natively compatible with an LS1.

Swapping an LS1 into a Saturn would require a significant and highly customized engine swap. It's a very involved project requiring extensive fabrication, custom mounts, wiring harnesses, and potentially modifications to the transmission, drivetrain, and cooling systems. The feasibility depends greatly on the specific Saturn model, and it's not a beginner-level project.