Athough they are fascinating I wouldnt say "any of Leonardos inventions". Many are drawings of thing that already existed, obsolete, or impractical, that helicoptor is not getting of the ground even with a modern engine, and giant catapults are not necesary when the canon has already been invented.
Leonardos scetches with the most potential are the hanglider, the parachute, the bycycle, and the hollow based pointed bullet.