Anki

Flashcards that appear right when you're about to forget.

PhET Simulations

Interactive science and math simulations from CU Boulder.

Project Gutenberg

Over 70,000 free public domain classic books.

Forvo

Native speaker pronunciation dictionary for any language.

Duolingo

The most popular language learning app — gamified and free.

Wikipedia

The free encyclopedia that anyone can edit.

Khan Academy

Free world-class education for anyone, anywhere.

freeCodeCamp

Free full-stack web development curriculum with certifications.