(iOS, Android; free)   The “MMO” in the game’s title stands for “massively multiplayer online” game, a genre that means thousands of people around the world are playing with you and against you at the same time. World at War is best described as a base-building and strategy game, where you form and train your troops before setting out to battle. A nice touch: Historical figures, including Gen. Dwight Eisenhower, make appearances.