BeTrains.Qt is a project mainly written in C++ and C, it's free.
Qt MVC framework for BeTrains applications using libqtrail.
BeTrains is a set of mobile applications providing easy access to public transport data. This specific project only contains the logic (the controller, in MVC terminology) which steers an application interface. An example of such an interface using this controller is the Maemo application, which you can find at the BeTrains.Maemo project. So, if you're just looking for a ready-to-use application, have a look over there.