In Civilization II, Adam Smith's Trading Company is a Wonder of the World that a Civilization can build. It grants the civilization that possesses it the ability to not pay for any of the City Improvements that usually cost one gold to upkeep.
In other words, it can save a lot of money for whoever controls it. Since most of the basic improvements in the game...granaries, libraries, markets, and the like, only cost one gold per turn, whoever has this wonder only pays for their more costy improvements.
The value of the wonder depends on when it is built. If it is built fairly early, before a civilization has many high maintanence improvements, it can reduce outgoing money to zero. As a civilization starts getting lots of things like SDI Defenses and Solar Plants, it gets less useful.