I downloaded just one new app for this thing, but I have already downloaded and used several of the other suggestions. I'm going to mention only a few, because the 23 Mobile Things project deadline is next week and I don't feel like I have as much time as I would have liked to mess around.
The new one I picked: Bill Nye the Science Guy. We are enthusiastic about science in my household, and I love encouraging my 4-year-old in critical thinking and scientific thought. This looks pretty cool, and it will be fun to try out some of the experiments.
I have used the Fooducate app before. It's helpful to get a quick snapshot of a product in terms of just how healthy it is -- not only in terms of calories and vitamins, but also if there are ingredients in the product that are concerning. For food logging or calorie counting, Fooducate wasn't compelling enough to pull me away from my old favorite app, My Fitness Pal.
Project Noah is a nature app that I had installed for a few years, but I never seemed to find a way to incorporate it into use. It's possible that it has changed or expanded, so I might give it another try.