Stack Merge 3D is a free puzzle game developed by VOODOO for iPhone. The game is simple yet addictive, and it challenges players to merge circles on top of towers. The objective is to merge two circles of the same value in a row and create a bigger circle. Players can discard circles they don't want and aim to reach a size of eleven to get a bonus.

The game features colorful graphics and a simple interface that is easy to navigate. The gameplay is fast-paced and requires quick thinking and strategy. With each level, the difficulty increases, and players must use their skills to merge circles efficiently. Overall, Stack Merge 3D is a fun and challenging game that is perfect for puzzle enthusiasts.