Steam, was released by Mayfair Games in 2009. It includes rules for the "Base Game," which is as or slightly less complex as Railroad Tycoon. The "Standard Game" rules are raise the complexity level to near that of Age of Steam. The expansion, Steam Barons, was released by Mayfair Games, also in 2009.
In August 2011, "Expansion Pack #1" was released by Mayfair Games. There are also some player-designed expansions for the Steam system available as print-and-play maps.