Besiege

Besiege is a puzzle game entirely base on physics. Some of the best games are based on great physics like Angry Birds, the Burnout Series, Star Wars: The Force Unleashed (the first one, not the second one; we don't talk about the second one). Besiege is a good example of building a game around it's physics engine. Along with a great physics engine Besiege let's you create your own craft from various tools to solve a puzzle. There is no one-way to complete the puzzle and that's what makes the game so addicting. You might find yourself building a machine in one level and thinking about the previous level and how you could have solved it in a more efficient way or a more destructive way.