Physics
Open source · offline · ages 12–14
1st placeHacktoberfest Hack Day Barcelona 2026 · Best Open-Source AI Project
Understanding is the key.
An offline voice tutor for kids aged 12–14 that runs on your own Mac.
You can delegate thinking,but you cannot delegate understanding.
127.0.0.1:5173■ OFFLINE
How a lesson works
It starts with “wow”, not with the answer
Every lesson card opens with a question from school science or math. The kid works out the cause out loud, step by step.
- 01
Wow
A question that shouldn’t work but does, with a scene from the world of the course.
- 02
Guess out loud
The kid says what will happen and why. Being wrong here is fine.
by voice - 03
The real cause
A short explanation of the cause, with a picture of the scene. Then the kid changes one thing and says what happens.
- 04
Explain a new case
A new situation, no hints. The kid explains it by voice and confirms what the computer heard.
by voice
why?
The tutor asks “why?” instead of handing out the answer. It judges the explanation by meaning against an answer key an adult approved, confirms a right cause, otherwise asks one question — and never gives the key away. It never grades accent or wording.
One course, one world
Pick a world when you make a course — Fantasy, Anime, Space or Cyberpunk. The world changes the scenes and pictures; the facts stay the same. Below: card 1 of “Why do some heavy things float?” drawn in each of the four worlds.
Local and private
The models live on the laptop
A child explaining out loud what they don’t understand is sensitive learning data. When the models run on the family computer, there is no third party to share it with.
01
Three open models, on device
Everything in the lesson runs right on the computer, through Ollama, whisper.cpp and MLX.
- Gemma 4tutor and course drafts
- Whisperspeech to text
- KokoroEnglish voice
02
The voice stays home
A child’s voice never leaves the machine. Recordings are converted, transcribed and deleted; there is no recording history. The server listens on 127.0.0.1 only.
03
No account, no subscription
Nothing to sign up for and no per-student token bill. Once installed, lessons keep working with the internet switched off.
Offline is the default and needs no key. Cloud models are optional: an Online profile with your own Anthropic or ElevenLabs key.
Make your own course
A course on anything you don’t get yet
Type a request in plain words, then pick a world — Fantasy, Anime, Space or Cyberpunk — who it is for, a kid or an adult, and a model. Local Gemma 4 drafts a short course with the same wow → guess → explain path and opens it when it is ready.
The app’s own estimate: about a minute locally, about 20 seconds online with your key. English only for now.
Biology
Where does a tree’s weight come from?
Math
The Growing Square Mystery
The repo has six English courses of five cards, plus a short Russian one that stays off while the interface is English only. Each course comes in one world, Fantasy. Every card of five of them — physics, biology, math, finance and critical thinking — was checked by an adult, fact → question → key; the physics, biology and math facts were cross-checked against OpenStax.
Install
One command on an Apple Silicon Mac
The installer prints what it will download before it changes anything, then sets up the tools, the locked packages and all four local models.
Terminal
# get the code $ git clone https://github.com/postnikov/understandity.git $ cd understandity # install and check everything $ bash scripts/install.sh
Then start it with bash scripts/demo/start.sh, wait for DEMO READY and open http://127.0.0.1:5173. Want to look first? bash scripts/install.sh --dry-run shows the plan and installs nothing.
Requirements
- macOS 15+Sequoia or newer
- Apple SiliconM-series Mac
- 32 GiB RAMor more
- ~30 GiBfree disk
Homebrew must be installed first. Internet is needed only for the install: the models are about 12.8 GB. Linux, Windows and Intel Macs are not supported by the installer yet.
Open source
Apache-2.0, built in one day
Built at Hacktoberfest Hack Day Barcelona on 24.10.2026 by Max Postnikov with AI coding agents, Claude Code and Codex: the code, the tests and the docs were written from scratch at the venue.
github.com/postnikov/understandityApache-2.0Honest status: a hackathon build
- Not tested with real children’s voices yet.
- There is no filter yet for what the model says to a child. It is required before real use with children.
- A course made with Make your own course is not checked by anyone.