So this is actually a novel that I saw recently in the bookshop, but without as much structure. This is not a game, but a novel (sorry!) approach to story-telling. You know when you're reading a book that has many viewpoints and one stops and you don't come back to it for a hundred pages to find out what happened? This fixes that! However, it is then left to the reader to define how the story is structured, without the writer and editor weaving the different elements together in a way that makes the most sense.
On the whole, it works, though it's a different experience to reading an actual book. Not so much choose your own adventure, but choose how long you follow each character for. Thankfully, it's a cracking good story. Apparently the app is much larger than the book so that it makes sense no matter how the reader weaves together the story. It also contains many notes from one of the characters that are alluded to in the story.
TL;DR a great book given in an unusual and engaging way.