I use CityMapper at least twice a day, every weekday. Once in the morning to check my journey is all good and no delays. Second, in the evening, on the way home from work, to check there are no delays! It’s an invaluable tool, and while not perfect, every time I’ve e-mailed the developers with a suggestion they have been extremely polite and taken it on-board.
CityMapper takes every bit of data they can get their hands on and then uses it to provide the user with information on how to get from A to B - whether it’s fastest to take a single tube, a bus and a tube, or simply just to walk.