Sado is an island off the coast of Niigata prefecture, Japan. It has never had trains (and likely never will), but it is a beautiful island and a fantastic place in many other respects. It would be even better if it had trains...
So the city council decided that Sado should have trains indeed, and gave a small budget to three companies to develop a rail network for tourists and freight on Sado, connecting the main ports (Ryotsu and Ogi) to the main tourist destinations and centers of (mainly agricultural) production.
AoS Sado doesn't deviate much from standard Age of Steam. It is a 3-player variant with a few twists and turns. Black cubes represent tourists, and consequently, these come in at the ports (Ryotsu and Ogi) only. Towns start with one cube each. And players/companies start with a little bit more money thanks to a government grant to promote tourism and the local industry (through railroad development). That extra money is necessary, however, as finances tend to be extremely tight in the beginning of the game.
-description from designer