TurboTrainer is a really simple application that loads in a GPX file and plays it back in real time, displaying the route’s current gradient on the screen.
The idea is to be able to use it with an exercise bike or turbo trainer to make your workouts a bit more realistic by following an actual outdoor route. You'd just watch the display and adjust the trainer's resistance according the displayed gradient.
I made it as an exercise in using Xamarin and ReactiveUI to write cross-platform MVVM. The project contains a WPF app and an Android app sharing practically all of the same code. There's a blog post if you want to read more about this.