'Four' is a collection of games intended to introduce board games to small children. They're a reinterpretation of classics, such as chess and shogi, but with changes that aim to make it as fun as possible to kids while allowing adults to have a deep and challenging experience.
Compared to the classic games, the four versions allow interactions very early in the game, which keeps children interested. They have movements and concepts relating to the classics, but are more dynamic, quicker and easier to understand. Also, they have a different setting, with cute and colorful animal play rather than the serious and militaristic tone classic board games usually have.
Finally, if you don't have a kid, don't worry - these are deep and challenging games even for experienced players, where one move can make all the difference.