Eagle is a geographical discovery concept app. It enables you to be able to point your phone in any given direction, select a distance of your choice and it will show you exactly which country or body of water is at the end of the sight line you just drew!
From here you can then find out more information about that country and see its own bordering countries.
The app is a brand new way of thinking about geography in a real-world space and really gives you a great sense of distance and how the shape of the globe and subtle changes in your heading can drastically change the sightline created.