Once you're out of school, it's all too easy to stop learning. You may not have any assignments due or tests to study for, but that doesn't mean you should stop exercising your brain. Doing exercises for your brain is just as important as it is for your body.

Strengthening your brain will improve your memory, concentration, ability to quickly form your thoughts, and so much more. And if you start training your brain now, you'll be sharper in your old age. Here are some great apps to get you started with daily brain training exercises.

1. NeuroNation

The NeuroNation app can power up your brain in multiple areas, including memory, concentration, and reaction time. When you first open the app, you are guided through a strengths and weaknesses test that tests your brain in four different areas. At the end of your test, your results are saved in the app and used as a starting point for your brain training.

Then, it's time to start. There are plenty of fun exercises to complete that feel more like games than educational exercises. While some games are reserved for subscribers, there are many great free choices too.

One of the coolest features of the NeuroNation app is NeuroBoosters, which are little exercises to engage both your brain and body in the middle of a stressful work day. These small exercises come with pictures and detailed instructions to make sure you're doing them right. There are 11 different exercises to cycle through.

Related: Meditation and Relaxation Apps to Beat Stress and Anxiety

If you purchase a subscription, you gain access to more personalized brain exercises and training. This training program is highly personalized and brings access to more courses. While a subscription is not necessary to enjoy this app, it does provide you with a ton of great extras that are worth the investment.

Download: NeuroNation for Android | iOS (Free, subscription available)

2. Train Your Brain

The Train Your Brain app has tons of fun and interesting games that are great for both adults and kids. Some games challenge your memory skills, while others test your problem-solving and spatial awareness skills.

Each game has multiple levels so that you are continuously challenged. There are only around 10 games in this free app, but since they progressively get more difficult and present a challenge, it won't feel like you're lacking content.

There's also a daily challenge to complete, prompting you to come back every day. And there's no limit to how many times you can go through each game. You can continue playing until you feel like you've worked out your brain enough.

The only in-app purchase is for removing the ads.

Download: Train Your Brain for Android | iOS (Free)

3. Memory Match

If you primarily want to build up your memorization skills, the Memory Match app is a great choice. This app is essentially a virtual memory matching card game, with levels that allow you to earn stars and monitor your progress.

You can choose to follow the levels mapped out for you, or you can create your own custom stages. With a custom level, you choose how many cards are on the screen and what's on the cards, like musical instruments or animals.

There's not a whole lot to this app, but it will help improve your memory. As you continue playing the game, you'll quickly see your memory improving. Plus, it's incredibly relaxing to play a simple game when you're stressed.

Download: Memory Match for Android | iOS (Free)

4. Lumosity

Similar to NeuroNation, Lumosity also offers a training test the first time you download the app. This takes your results and lets you know where you stand compared to others your age, highlighting which areas you need to work on the most.

Every day, you have access to a basic workout for free that includes three different cognitive games. These three games change every day, but you play the free offerings as many times as you want within the day. The best features of the Lumosity app are only available to Premium members who pay for a monthly or yearly subscription plan.

If your goal is to only exercise your brain a little bit every day, the free version is plenty. But if you really want a personalized training plan that focuses on your weak areas, the Premium version might be worth it. You can always try out the Premium version over a two-week trial and cancel it if you don't think it's worth your money.

Download: Lumosity for Android | iOS (Free, subscription available)

5. Mnemonist

Mnemonist is another fantastic app for improving memorization skills. With it, you are given a series of words and then must remember all of them at a later time. There's a timer that counts down, so you only have a limited amount of time to look at and memorize the list.

Related: Want to Improve Your Memory and Recall? These Tools Might Help

Sometimes you can only see one word per screen, while other times you can see a long list of words. As you progress to higher levels, the amount of words you have to memorize gets larger. What's neat about this memorization app is that you'll eventually have to use some kind of trick to remember all the words.

Simply memorizing the words may work in smaller numbers. But when you have long lists, you need a mnemonic device or other memorization technique to help you. For example, look at the first two words in the screenshot above: button and remote.

You can remember those two words by remembering something like "Push the button on the remote." The same concept applies to the rest of the words.

Download: Mnemonist for Android (Free, in-app purchases available)

Strengthen Your Brain Every Day

Exercising your brain doesn't have to take up a huge chunk of your time. You only need about 10-15 minutes of brain stimulation daily to start seeing results. Of course, if you have more time to train your brain, go for it. But if you only have a few minutes here and there, that's all you need.

In addition to strengthening your skills with memorization, problem-solving, logic, and speed, it's also important to remember to strengthen your ability to relax and unwind. Stress takes a toll on our bodies, both physically and mentally. So make sure you also have a great calming app to let go of stress and maintain a positive outlook on life.