Dictionary.com
You can look up nearly any word, and whether you need a dictionary or thesaurus, you'll find what you're looking for.
Available from: iTunes, Google Play
Lumosity
Designed by neuroscientists, Lumosity is meant to improve your core cognitive abilities. It hones memory and attention to detail through a variety of mind games.
Available from: iTunes, Google Play
Wikipedia
The site's official app provides access to the catalog of more than 32 million disputable articles, each offered in more than 280 languages. It has additional options for quickly sharing articles on social networks or saving for offline use.
Available from: iTunes, Google Play
Coursera
With more than 200 free courses covering more than 20 subjects, Coursera allows you to engage in a variety of courses from universities and institutions around the globe. Enroll in classes, stream and download lectures and watch content.
Available from: iTunes, Google Play
TED
The TED app gives you access to the entire library of more than 1,700 TED Talks videos. View intriguiding presentations and ideas from tech geniuses, business gurus, musical legends, etc.
Available from: iTunes, Google Play
Khan Academy
This app provides more than 4,000 free downloadable videos on a variety of subjects including high school math and science to art history and computer science. You can also track your progress and unlock basic achievements.
Available from: iTunes
StudyBlue
Create and share a variety of mobile flashcards, study guides and quizzes. You can also choose from a large collection of student-authored flaschards.
Available from: iTunes, Google Play
Duolingo
Duolingo allows you to translate real-world texts in your desired language of choice. It can translate web pages and other documents into many languages. It also offers language courses at all levels.
Available from: iTunes, Google Play
Learnist
Learnist is like a social network for knowledge. This app lets you browse an organized collection of text and video content, much of which is sequenced into lessons covering thousands of topics.
Available from: iTunes, Google Play
Scanner Pro
This app allows you to scan and convert physical documents (like pages and pages of notes!) into PDFs, which you can then email, print or upload. The app can automatically detect edges and borders, keeping cropping to a minimum.
Available from: iTunes