LeetCode
FreeThe standard platform for coding interview preparation: thousands of algorithm and data structure problems with an in-browser judge, discussion solutions and company-tagged question lists. Free tier covers most problems.
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Gamified language learning across 40+ languages: bite-sized lessons, streaks, leagues and spaced repetition. The free tier includes the full course content with ads and limited hearts.
Free world-class courses from arithmetic to college-level math, science, economics and humanities: video lessons, mastery-based practice exercises and progress tracking, with no ads and no paywall.
Online courses and degrees from universities and companies — Stanford, Yale, Google, IBM. Most courses can be audited free (videos and readings); certificates and graded work are paid.
Flashcard platform with hundreds of millions of user-created study sets across languages, science, history and test prep, plus practice tests, matching games and learn mode. Free tier covers creating and studying sets with ads.
Web companion to Anki, the reference spaced-repetition flashcard system: review your decks from any browser and sync progress across desktop and mobile. A free account syncs seamlessly with the open-source desktop app and its thousands of community shared decks.
Minimalist typing test with live WPM, accuracy and consistency stats, dozens of modes and themes, and detailed progress history. Open source, free, no account required to practice.