Railboard is only available on iOS right now because the founder of Railboard (me!) is an iOS Developer, so the iPhone app was made before the Android app.
It is of course a very high priority to make the Android version of Railboard. Android customers make up approximately half of the people using trains, and being unavailable on Android makes it much harder for people to share Railboard with others.
Once Railboard is sufficiently profitable to fund the development of an Android app, you can be assured that it will become the number one business priority!