Zachy the Robot - Episode 1: The Leaning Tower of Robocity ($1.99) by GenevaMars, LLC is the first installment of Zachy the Robot and his friends, the Ultimate Repairbots.
The animated characters teach the concept of structural support, especially in buildings. There is even a song or two along the way to provide some review of the concepts. This app is similar to the Brainpop apps, but surpasses them by adding an interactivity component.
The app is a combination of animated sequences, combined with applying concepts presented by the characters.
For example, as the Repairbots are on their way to fix the leaning tower, they stop because a lamppost is blocking their path. Toby the Toolbot arrives to present a selection of shapes that can be chosen to keep the post upright.
The lesson the characters learn from supporting the lamppost will pay off later when it comes to the tower. There is an icon of Zachy in the upper left corner, which brings up a chapter selection option. Each chapter is about four minutes long.
Overall, this is an interesting story with enjoyable characters and a special message of observing things in action for problem solving. At $1.99, this app is a little pricey because the story does not take long, and there is little variation in gameplay. However, kids may not mind watching the animations over and over.