This is a great "Rube Goldberg" style problem solving app for kids.
The thing that I really like about it is that (in comparison to other Rube Goldberg apps) is that it starts very simply with a limited number of pieces to use. It allows the kids to learn how each piece works in the correct directed context. There is an opportunity to earn 1-3 stars each level.
This puts the kids in a "prototype --> refine" state of mind to problem solving. This is a great way to start them on the right path to learning. I really like the progressive nature of the difficulty. My 4 year old does very well with this and will do better in the future on more complex levels.
There are some good physics principles here. So far we've seen the law of gravitation, the law of reflection, density and a host of other stuff. This is a great introduction to real physics principles.
How I Use It
The app is good for pre-K through grade 5. It is a "Rube Goldberg" style problem solving, drag and drop app. I use it specifically with my own 4 year old who digs it a ton. It is really an individual activity although he and I talk about his decision making while he plays. The levels get progressively complex but I have seen my son grow in his ability as the levels get higher.
In the beginning there are not many ways to solve solve the levels; which I like. As the levels increase there are multiple ways to solve. I like to ask my son if he can solve it a different way.