Source: Wikipedia, "Railroad Tycoon (series)", available under the CC-BY-SA License.
A sequel featuring improved graphics and more complex gameplay, Railroad Tycoon II, was published by Gathering of Developers in 1998 after PopTop Software acquired rights to the name from Microprose, Sid Meier's original company which he himself left a year earlier to form Firaxis.
Some features of the first version are missing in this sequel, such as the ability to build tunnels and signal towers, but many new possibilities were added, such as the ability to have unlimited money, trains, and train routes, much better control of routes, dozens of new maps, and the ability to create and modify scenarios and maps.
The Dreamcast version was in full 3D.
There are dozens of new scenarios to play including ones in Africa, North America, Germany, the Swiss Alps, the jungles of South America, and even several places around the world in a possible future where Earth's oceans have risen. Most of the ones in Railroad Tycoon 1 are in Railroad Tycoon 2. There are also many more first and second century campaigns to choose from than in Railroad Tycoon 1.
An expansion pack, Railroad Tycoon II: Second Century, was later added which contained new scenarios focusing on modern and near-future times, plus added new elements to the economy. The game and its expansion were repackaged together in the Gold Edition and then, with 50 additional user-made scenarios, into the Platinum Edition.
A short lived, budget title, named the Millennium Edition went on sale in 2000. It featured many scenarios and features of The Second Century, but no map editor. It had no instruction booklet and was sold only in a jewel case.