Your vote:
Train simulator with a collection of routes, rolling stock, and activities.
A program to interactively enable/disable Microsoft Train Simulator routes.
Economic simulation in which you can prove your skills as a leader.
This is a open source version of Transport Tycoon Deluxe. OpenTTD will run on almost every pice of hardware.
You need original TTD files to run OpenTTD.
Warning: extremely addicting!