OpenTTD - An open-source clone of the classic game ...
Open Rails - Open Rails is an open source simulator that is designed to run Microsoft Train Simulator content.
Micropolis - Micropolis is the open source version of SimCity Classic from Maxis, developed by Will Wright and Don Hopkins.
Trainz Simulator - Trainz Simulator is a commercial train simulator from Australia.
Simutrans - Simutrans is an open-source transport simulator.
BVE trainsim - BVE trainsim is a train simulator based on the point of view of the train operator.