As a native New Yorker - and by extension, a person who's quite familiar with subway systems - I found the concept of Mini Metro to be instantly appealing. Of course it's only available on Steam. Or at least, it was.
Dinosaur Polo Club has been hard at work bringing the stylish, minimal, and exceedingly clever Mini Metro to iOS. The basic idea is that you have to run a metro subway system by creating train lines that reach different stops, and ferrying riders around before they get too cranky after waiting an age and a half to get to their destination. Easier said than done, obviously.
The build I was able to get our hands on is still in the early stages but it already plays quite well on a touch screen. Dragging new lines around or editing existing ones is pretty fluid, and adding new trains and train cars is quite easy. Keeping everybody happy by balancing your subway lines, not so much.
Mini Metro will be coming to iOS (definitely on the iPad and potentially on the iPhone as well) sometime in Q4 later this year. Keep your eyes peeled for this one. Seriously, they pretty much had to wrestle the iPad away from me after the demo.