Just like our body, our brain also needs a workout from time to time to stay sharp. In the past few years, we have covered a whole host of math and brain games that can do just that. Einstein Brain Training is also worth a look. It tests your logic, memory, calculation, and vision with fun exercises.
The app dynamically adjusts difficulty as you practice. It provides you with player statistics and high scores. These exercises are not hard to complete, but they do give your brain quick stimulation. Einstein Brain Training is available for under $3 at the time of this writing.[HT]