Mr. Nussbaum Learning+Fun offers an amazing array of free K-8 learning resources and games about math, language arts, history, the USA, geography, science, people, holidays, and more. You can filter by topic and grade.
But the best part is that the games are not simply glorified quizzes. They have real-world meaning.
For example, the 5th-grade fractions game, “Tony Fraction’s Pizza Shop”, requires the player to first choose a pizza size, then sprinkle toppings on a pizza according to the customer’s request…for example 7/10 cheese, 1/5 pepperoni, 1/10 mushrooms.