SUM! is both a mathematics app for children and a brain-teaser for adults. It teaches kids how addition works in a playful manner by dragging a number to merge (add) with another character. For adults, it is a quick and exciting calculation puzzle comparable to the famous game Tetris. The game is based on the idea of personifying the numbers in the game to make them easier to identify; just as each child has a unique individuality, each number has its own face and personality. The result is that children identify with them and thus become interested in mathematics.