Education

SentenceCoach

Fixes a learner's Mandarin with the smallest change and says why

It keeps your sentence and changes only what is wrong, so you learn the rule you broke instead of receiving a rewrite you could not have produced.

If your team is about to argue over whether 82% beats 80% on an eval, there is a page here that settles it with error bars you can move yourself.

netties

Draw interaction nets, write their rules and watch them reduce in the browser

If you are working through Lafont's interaction combinators, this lets you test a rule on a real net instead of on paper.

Warsaw in voxels

Walk central Warsaw as Minecraft-style blocks built from open map and LiDAR data

It shows how far public geodata plus an AI-assisted first draft can get one person toward a walkable city model, and the code is open to borrow.

hjkl

Learn Vim motions by finishing small edits in an editor in your browser

Ten minutes a day here builds Vim muscle memory without risking a real file, and it accepts any edit that reaches the target text.

Wikihack

A scrolling feed of the Wikipedia pages Hacker News keeps linking to

Every article comes with the HN threads that cited it, so the reason it is interesting arrives along with the article.

syscall.sh

Linux syscall tables for 27 architectures, by kernel version, with a JSON API

When you are writing assembly, a seccomp filter or a port, it answers which number, which register and since when, for the CPU you actually target.

LearnHarness

A desktop tutor that starts by finding where your understanding stops

It locates the edge of what you already know and keeps that map between sessions, which is the part a fresh chat window throws away every time.

HackerBooks

Every title two or more HN readers have brought up since 2007

It turns a habit — screenshotting book titles out of comment threads — into a searchable index of 16,500 titles, each linked back to the people who argued for it.

BBRouter

Breadboard wiring you can get wrong in a browser instead of on your desk

If you have ever lost an evening hunting one miswired jumper, this models wire length, thickness and bends so the mistake shows up on screen first.

Doomformer

Compiles small neural networks into DOOM maps you can walk through

If you have ever wanted to see what a transformer is actually doing, this one is a level you can walk around in while it reads your handwriting.

Redible

A reader and narrator for seven languages, with a tutor you can ask aloud

It makes a whole book, rather than a graded lesson, the unit of practice, and the voice mode means that practice survives a commute or a walk.

Encarta 95 Web

Windows 95 boots in a tab with the encyclopedia already open

A quietly useful lesson in cheap emulation: a RAM snapshot and 256 KB on-demand chunks let a static page serve a 1995 CD-ROM with no server behind it.

Drop7 Research

An open hunt for a million-point policy, playable as you read

A rare piece of agent-assisted research you can audit end to end: frozen protocols, dated cohorts, open code, and the same board in front of you as the solver.

Little Story Machine

A cut-out paper contraption that lets a three-year-old pick who meets what

Seven of the fourteen printables need no sign-up at all, so A4 or US Letter can be on the printer before the child loses interest.

How It Evolved

Nine thousand years of five religions on one timeline, every date sourced

Every label is dated to the earliest surviving evidence rather than a claimed origin, and opens the chapter that cites it.

Pistio

A free French tracker for alternance, internship and job applications

French students juggling dozens of alternance applications get a pipeline that tells them who to chase today, free and without AI.

Quix

Ten questions, ten seconds each, against real people in a browser tab

It brings back the head-to-head phone quiz that QuizUp fans lost, with India-first topics and a one-off fee instead of a subscription.

Moodteca

Pick a few moods and covers, get books that feel the way you want to read

It replaces genre shelves with five axes of how a book feels to read, and adds wildcards that flip your surest choice so you stumble on something new.

Permit Pending

A city builder where you are an elected mayor, not a god

It turns the dry mechanics of zoning, hearings and appeals into a game, which makes it a surprisingly good teaching tool for anyone who has wondered why housing takes so long to build.

Learncroc

Short, playable lessons with spaced review, built from the docs you must know

It turns the RFC or onboarding doc you skimmed into something you can explain a week later, without sending company docs to anyone's server.

Penmentor

Pen your maths in Xournal++, press a key, get teacher-style ink marks back

For self-taught learners and homeschoolers, it turns your coding agent into a tutor that nudges with hints instead of handing over the answer.

Groovemap

Thousands of drum grooves you can play, dissect and export as MIDI

A drummer or producer hunting for a feel can hear it, see each limb's part and drop it into a DAW in under a minute, with no account.

Yara Reads

A children's story reader where every tapped word breaks into its sounds

It turns the gap between learning phonics drills and reading a real book into something a six-year-old can cross alone, and the code is MIT.