I like to focus on digital tools and games which are free, however, this one I couldn't resist.
“Crayon Physics Deluxe is a 2D physics puzzle / sandbox game, in which you get to experience what it would be like if your drawings would be magically transformed into real physical objects. Solve puzzles with your artistic vision and creative use of physics.” http://www.crayonphysics.com/
The aim of the game is to create a path for the ball to move and roll over the star. There is a range of levels to work through.
This is a great game for problem solving, decision making and creativity. As the title suggests it can be used to understand different rules of physics such as the effects of gravity, size and weight. It is great for all ages.
This link shows videos of the game in use.