A free program for Android, by Marie-Luise Hanna Frieda Dr. Könneker.

Quell your boredom with Book of D, a mobile game that tests and hones your intuition. The objective of the game is to find all the matching images among a series of letters and numbers. Book of D  doesn’t have a hints system, so you really have no choice but to rely on your intuition. It also doesn’t seem to feature an in-game timer, which is a relief for gamers who want to take their time. In addition, the graphics are well-made and eye-catching to draw you into the game. 

Whether you’re a casual player or someone looking to widen your gaming repertoire, Book of D is the right app for you. As of this writing, it is compatible with devices with Android 7.0 and newer.