You can also get OpenTTD on Android. The android version is basically the desktop version slapped onto the phone so it is awkward to use via touch screen. But it is good if you need to feed your model railway obsession while on the go. Also a similar open source game that I discovered before OpenTTD is Simutrans.
This is fantastic. I can't count the number of times I have stared at a man page trying to figure out how I am supposed to use a command.