We -two chess teachers- have developed an app to study with PDF books, 200.000+ PGNs library and Stockfish 6 -latest version of strongest chess engine for Android- to analyze and play against. This is a free app so please check it out. We developed it in a manner that every level player from beginner to tournament players
can get max use of. Especially tournament players will love it because of it's great features. As you go through it, you will see this is the best chess tool on Android. Here is the link to Google Play Store:https://play.google.com/store/apps/details?id=org.savantedroid.chessclassdemo
Also your opinions are very important to us. Please give us a review so we can develop it even further.