Art Of Game Design: Lenses
https://play.google.com/store/apps/details?id=com.schellgames.deckoflenses&hl=en

It is an app which allows you to pick various “lenses” (or angles/points of view) from which you look at the design of your game. These are questions which you should ask yourself to make your game better.

To fully take advantage of this app I would recommend reading the following book:
https://www.amazon.com/Art-Game-Design-Book-Lenses/dp/0123694965

Yes, that is an app for this book 😀

There is also a Twitter bot account you can follow to receive these questions right into your feed!

https://twitter.com/BotofLenses/status/883531712315232257

Got a practical app or software for gamedevs? Have a book to recommend?
Let us know in the comments!