1. Fit Brains Trainer

There are over 360 puzzles and games on this app you can try in order to train your brain to think a little more quickly. There are plenty of gaming levels where you can increase the level of difficulty to your liking.
itunes.apple.com
play.google.com

2. Memory Trainer

This app takes you through a series of exercises that help you remember things from phone numbers to tasks you need to complete. The exercises help you recall information more easily.
play.google.com

3. Happify

With this app, you may push the unhappy thoughts out of your head by replacing them with happy thoughts. There are quizzes, polls and a controversial gratitude journal.
itunes.apple.com
play.google.com

4. Eidetic

This app helps you train your brain with spaced repetition. With it, you will learn a technique that allows you to quickly memorize phone numbers, names and your friend’s birthdays.
play.google.com
itunes.apple.com

5. Lumosity

If you want to improve your memory, flexibility of thinking, processing speed, attention or problem solving skills, then try the games on the Lumosity App.
play.google.com
itunes.apple.com

6. Personal Zen

This app will help you maintain a calm state of mind. It will help you relax so that your brain may get a little respite before you challenge it with something new and fresh.
itunes.apple.com

7. Elevate

This one is a brain-training program designed to improve your focus, your speaking abilities, your mental processing speed, memory, and your math skills. Each user is provided with a personalized training regimen that adjusts over time.
itunes.apple.com

8. Braingle

Improve your reasoning skills with this app by working through a series of optical illusions and riddles. There are over 15,000 brainteasers and the app is free too.
itunes.apple.com

9. 150+ Brain Teasers

Just like it says, the app has 150+ brainteasers, most of which are text based. They may help keep your brain active and will help you look at things a different way.
play.google.com

10. Mind Games

There are a wide variety of tools on this app that help you train different cognitive abilities. They have categories such as face memory, path memory, speed trivia, and many more.
itunes.apple.com
play.google.com

11. Relief Link

This is a mood tracker that was first invented to try and lower the number of suicides. It tracks your mood, and with the data, you are able to train your mind to stay out repetitive low moods.
itunes.apple.com

12. Brain It on

One of the fun things about this app is that many of the physics puzzles have more than one answer. There are plenty of different games to keep you occupied.
itunes.apple.com
play.google.com

13. Brain Trainer Special

This is a collection of games you can use to improve your thinking skills with a few simple brain-training exercises.
play.google.com

14. Cognifit Brain Fitness

With this app, you can train your brain on the go, assess your brain, discover your cognitive ability and assess you mental health. There’s personalized training function or you can play single games.
itunes.apple.com

15. BrainHQ

This app comes from Posit Science. It helps improve your thinking speed and your memory. It may even help focus your attention. Some say it reduces your chances of accidents.
itunes.apple.com

16. Positive Activity Jackpot

The app uses a behavioral therapy called pleasant event scheduling (PES). People originally (and still do) use the app to build their mental resistance and overcome depression.
play.google.com

17. Brain Dot

The game looks simple, but as it goes on it becomes increasingly more challenging. It forces you to improve over time by improving your cognitive abilities.
play.google.com

Any others you’d recommend?