Jet Moto 2124 is the cancelled 4th episode in the Jet Moto (Jet Rider in Europe) series of futuristic racing games, that was in development for the original PlayStation as the previous 3 games. The gameplay differs from that of a traditional racing game with cars, as players instead control hoverbikes which hover close above the ground and can be driven over both land and water. [Info from Wikipedia]
Soon after finishing Jet Moto 3 the team started to work on the sequel: JM2124 was set in the future and it had 16 tracks to play through, across the entire solar system from the Moon to Jupiter. Even if Jet Moto 4 was almost finished, after the low sales of the third game they decided to kill the new project and the development was stopped. A playable build exists somewhere out there and maybe in the future it could be preserved somehow.
Thanks to Hey Hey for the contribution!