A free app for Android, by LoadComplete.

If you are looking for a new challenging game that will test your strategy skills, this free android game is worth the try. Merge Tactics is a deceptively simple yet challenging defense game with delightful growth, strategy, and customization elements. Set up your forces however you want as you work to defend yourself against a variety of invaders. Create custom battle decks and strategies, merge blocks together to make more powerful units, collect blocks of various kinds, and grow your castle and characters with gold and artifacts from battle– Merge Tactics has something for everyone!

The game is free to play, but you can purchase certain items with cash to make it more enjoyable.