BAHN is a program for the simulation of train systems.
It's predecessor was made for streetcar nets only, but today you can built railway lines, too. If you are interested in Model Railroading, but you don't have a Layout, then BAHN can help. Even of you do have a Layout, it is often useful to model changes before you make them. With this program several hundred kilometers of track and over 1000 trains (simultaneous running) can be modeled on the PC, even a Laptop!
If you have been disappointed that your city's public transportation system doesn't run often enough, or doesn't run at all, BAHN lets you see how things could be if you were in charge! With this program train systems of quite respectable size can be built up and put into motion (eg the metro of London, Paris or New York, the Streetcar systems of Dresden or Leipzig, or of the entire rail system of Saxony).