Summer is finally here. It’s time to close those books, log out and get outside. Maybe you have plans to travel or lounge on the beach with a book.

But let’s be honest: You will probably spend more of your free hours on your phone than anything else. Why not use some of that time productively?

Here are a few apps that will keep your mind sharp and phone usage guilt-free this summer.

Math and science

Do you struggle with or are fascinated by math or science? If so, Brilliant was made just for you.

The Brilliant app is designed to stimulate interest in and comprehension of science, math and technology. Through interactive microlessons, Brilliant creatively clarifies various concepts for novice mathematicians and scientists. But more seasoned STEM learners will be challenged too.

I think a first-rate feature of Brilliant is the daily challenge. Each day, there is a new question to engage your problem-solving skills for a few minutes or up to a few hours. If you get stumped, the community is a great resource for explanations and discussion.

Introductory lessons and daily challenges are included in the free version of the app. The premium subscription provides complete access to all lessons and a daily challenges archive.

Brilliant is downloadable on iOS and Android devices. A web-based version is also available at Brilliant.org.

Computer science

For all things computer programming, count on the SoloLearn app.

SoloLearn teaches both programming concepts and languages. Whether you want to be a professional programmer or a casual tinkerer, SoloLearn is a great place to begin coding.

To date, the platform offers courses in 10 different programming languages, including C++, Java and Python 3. There are also lessons in data science and web development.

The programmers at SoloLearn understand the best way to learn how to code is to code. I agree. The platform includes a basic programming environment so you can practice and show off your coding skills.

SoloLearn is available for iOS and Android. It’s also on the web at sololearn.com. The free version has all the main features, while the premium service provides an ad-free experience and a few extras.

Languages

Language learning is a popular category of apps. Although I’ve tried several different ones, I find myself returning to Duolingo.

If you’ve tried learning a new language in recent years, chances are you’ve heard of—if not used—this free multimedia app. It has instruction modules for two dozen popular languages, including Spanish, French and German. “Game of Thrones” fans can even brush up on High Valyrian.

Duolingo lets you set daily goals as you work through its lessons on speaking, reading and writing in a foreign language.

The app also has unique supplementary features. Its podcasts and quirky interactive stories help sharpen listening and comprehension skills.

Duolingo is available on iOS and Android (and on the web at duolingo.com). The Duolingo Plus subscription provides an ad-free experience and a few extras.

History

The last app on my summer shortlist is The History of Everything. For me, the app rescues fascinating history from flat, boring presentation methods.

The app features a unique scrolling timeline that displays events chronologically. It uses original, animated images. It makes the most of the touchscreen capabilities of your device, letting you lengthen or shorten the visible time frame.

Although the app offers mostly popular history—not the deep dive of college history courses—it’s a fun way to learn something new. It is free to download on iOS and Android devices.