This is college coursework in an app. If the thought of doing homework or racking up a hefty sum of student debt doesn't appeal to you, here's another option— or at least a supplementary one. The Great Courses app offers lectures from expert professors, covering a wide variety of subjects, including literature, history, business, math, music, cooking, and even professional skills. It enables users to download or stream courses. The lectures are professionally made and presented clearly, with visual aids when necessary.

While the app itself is free, you'll have to pay for individual courses. There is a free trial, though, and courses go on sale relatively frequently (70 percent off in some cases). Plus, your smartphone probably weighs a lot less than a textbook.

The app is available on iTunes and Google Play, and users can stream the content on Apple TV, Amazon Fire TV, Roku, and Chromecast.