Free online learning tools

Visual music theory site that shows harmony as colored flags and piano-roll views of songs.

Technical ear training exercises aimed at audio work, from an open-source project.

Drag-and-drop block coding for Arduino with a simulator for the circuit.

Upload a PDF and Claude writes a flashcard deck from it, which you then practice through games, quizzes and an XP system.

Use area tiles to multiply and factor polynomials visually.

Drag points and see the fitted line, residuals and correlation change.

Interactive demo of how model complexity trades bias against variance.

Animated explanation of k-fold cross-validation and why it is used.

Step-by-step interactive explanation of how a decision tree picks its splits.

Scroll-driven visual essay on fitting a line, loss, and gradient-based training.

Interactive walk-through of neurons, layers and activation in a small network.

Interactive illustration of precision, recall and how they trade off.

Visual essay on how bagging many trees makes a random forest.

Move a classification threshold and see the ROC curve and AUC respond.

Add bonds and lone pairs around a central atom to see VSEPR molecular geometry.

Stimulate a neuron and watch ion channels and the membrane potential during an action potential.

Uses area models to show multiplication and factoring of whole numbers.

Places masses on a plank to balance it and discover the lever principle.

Balances scales to build intuition for solving equations.

Explores fractions with shapes, number lines and matching games.

Feeds numbers or pictures through a function machine to infer the rule.

Shows how slope and intercept shape a line, with challenges for slope-intercept and point-slope forms.

Compares paint mixes and necklaces to explore ratios and proportional reasoning.

Animates an email's path through sender client, mail servers and receiver client, with an AI-generated explanation of each step.