Resources
Helpful free tools.
Everything here is free and has earned its place.
Math
Khan AcademyVideo lessons and practice for every topic from algebra to calculus.↗DesmosA free graphing calculator in the browser. Great for seeing what an equation actually looks like.↗Wolfram AlphaType in a problem and get the steps. Use it to check your work, not to skip it.↗Paul's Online Math NotesClear written notes and worked examples, algebra through calculus.↗
Science
PhET SimulationsInteractive simulations for physics, chemistry, and biology. See the concept move.↗Khan Academy ScienceFull courses in biology, chemistry, and physics.↗LibreTexts ChemistryA free, thorough chemistry textbook online.↗Crash CourseFast, entertaining overviews. Good for the big picture before the details.↗
French
WordReferenceThe dictionary we use. Its forums answer the "why is it phrased like that" questions.↗Lawless FrenchClear grammar explanations with practice, organized by topic.↗TV5MONDELearn French with real videos and news, leveled from beginner up.↗Lingolia FrenchQuick grammar reference with exercises and answers.↗
Coding
freeCodeCampHands-on, project-based coding curriculum. Completely free.↗CS50Harvard's intro to computer science. The best starting point if you want to go deep.↗Python TutorialThe official Python tutorial, straight from the source.↗ExercismPractice problems in dozens of languages, with free mentor feedback.↗
Chess
Study techniques
Three ideas beat all the tricks: active recall (test yourself instead of rereading), spaced repetition (review on a schedule, not in one cram), and past papers (practice the exact format you will be tested on).