Actually learn something

Maths explained by intuition first and formulas second, by someone who clearly resented how he was taught it.

The personality model psychologists actually use, in a clean 120-question version with a proper breakdown of every facet.

Centuries of natural history books scanned page by page, including illustrations nobody has looked at in decades.

Cyberpunk progression game where the way forward is writing real JavaScript to automate your own hacking. Learning it is the game.

The volunteer lightning detection network behind most live strike maps, with raw data and instructions for building your own receiver.

Monkeys pop balloons along a fixed path, and the upgrade trees behind that sentence are deep enough to justify the reputation.

Roll a rectangular block across floating tiles into a hole, with switches placed to force you to think in three dimensions.

Plain, well-sorted illusion collection with the explanation directly underneath each one, from café walls to impossible triangles.

Tens of thousands of riddles, brain teasers and lateral thinking problems submitted by users since 1999.

Dual n-back, the working-memory drill psychologists keep arguing about, implemented properly and charted over time.

A scrappy free collection of brain teasers and n-back drills that has been quietly online since long before the app stores existed.

Where the bridge world actually plays: free tables at every hour, tournaments, and teaching rooms of remarkable patience.

One page per leak channel — WebGL, canvas, WebRTC, DNS — each showing precisely what your browser hands over without being asked.

The Second World War version of the same slow, sprawling map game, with research trees and alliances that rarely survive contact.

Type any web feature and see which browsers support it, version by version, alongside how many people actually use each one.

Two near-identical interfaces, one of them subtly wrong. Getting past the third level takes an unreasonable amount of care.

Per-component checklists — buttons, forms, cards, empty states — covering the things everyone forgets until review.

A stocked chemistry bench in the browser where you can mix reagents and get it badly wrong at no cost.

Chess tactics training with a rating that goes down, plus an endgame trainer that reveals exactly how much you do not know.

The default chess address for most of the planet, with a bot for every skill level and puzzles that will quietly humble you.

Nearly a million recorded games from four centuries of chess, replayable move by move, with the real arguments in the comments.

Long branching novels where your stats matter and the prose does not embarrass itself; a good number play free in the browser.

Fourteen small experiments — spectrogram, harmonics, arpeggios — that explain how music works by letting you break it.

A history map with a timeline slider, layered with rulers, religions, battles and linked encyclopedia articles.

Scanned American newspapers from 1770 to 1963, full-text searchable, which is a dangerous thing to discover on a weeknight.

Five photographs, one question each: what year was this taken? Points scale with how close you land, and the cars always give it away.

Video walks through a real city, and your job is to work out which one from the shopfronts, number plates and pedestrians.

A global membership devoted to looking up, with a cloud of the day and a manifesto against blue-sky thinking.

The word-association board game in a free, well-built online room: two spymasters, one grid of code names, nothing to install.

Run a coffee stand for fourteen days, adjusting recipe and price daily, and learn more about margins than from any lecture.

A plain, ad-free bank of cognitive tests — n-back, digit span, Stroop, mental rotation — that keeps a history of your scores.

Match hue, saturation and complementary colours against a target, one exercise at a time, scored out of a hundred.

Palette generator trained on photographs and films, so the colours it suggests look like they came from somewhere real.

Petabytes of crawled web pages released free for anyone to analyse. Most of the language models you have used started here.

Interactive models of what complexity science likes best — epidemics, flocking, synchronisation, forest fires.

Sixteen words, four hidden groups, four mistakes allowed. The traps are the entire point and they are very carefully set.

Risk on hundreds of user-drawn maps, played slowly against a community that has been arguing about dice odds since 2006.

Guess the secret word and be told only how semantically close you got. Rank 4,000 feels like progress, and it very much is not.

Home of Conway's Game of Life — pattern archive, wiki and a board for setting your own cells running.

Recipes laid out as a table of operations instead of prose, so you can see at a glance what combines with what and when.

Nest and feeder cams run by the Cornell Lab, with ornithologists in the chat explaining what the bird is doing and why it matters.

The EFF's test showing how uniquely identifiable your browser is from fonts, plugins and screen size alone. Most people are one in millions.

The entire tower defence shelf in one place, sorted by how many people are currently playing, none of it requiring an account.

Scores films for you by finding users whose past ratings track yours, then weighting their opinions. Recommendation with the maths shown.

Wordle in reverse: you are handed the green and yellow clues and have to reconstruct the guesses that could have produced them.

An explorable on how ideas and riots spread through a social network, with the contagion thresholds under your control.

Recreate a target image in as few characters of CSS as possible, then watch somebody do it in half as many.

Tower defence from the villain's side, defending your gems from heroes using demons, orcs and the undead.