A free app for Android, by Chess King.

Chess Combinations is a free chess program for players of all levels, which includes 1300 exercises, classified into 40 tactical methods and motifs.

The program is suitable for beginners as well as for experienced players. Each lesson contains an explanation of the method, a description of the tactic, and an analysis of its implementation in an actual game.

Each lesson also contains hints and suggestions, which will help you improve your chess knowledge, learn new tactics, and consolidate the acquired knowledge into practice.

The program contains a theory section, which explains the methods of the game at a certain stage of the game, based on actual examples. The theory is presented in an interactive way, which means you can not only read the text of the lessons but also make moves on the board and work out unclear moves on the board.