OpenTTD

OpenTTD stands for Open Transport Tycoon Deluxe. Basically it's a game where you build roads, train tracks, canals, and airports, to connect different towns and industries. For example, you can make a bus route between two cities to transport people. Or make a train route between a coal mine and a power plant. Then you try to get some money. It's pretty difficult. (For me.)  http://www.openttd.org/en/