Invite-only beta · built for iPhone

Reading isn't understanding. Explaining is.

Mental Gym is a 15-minute workout for your mind. Learn one idea about AI, tech, business or science, then recall it, explain it, apply it to a problem you've never seen and defend it against an AI coach that doesn't hand out free points.

How it works

Free during the beta · Every request is reviewed by a person · No credit card

15 min
One idea, start to finish
6 reps
Learn → recall → explain → apply → defend → results
5 modes
Learn, models, argue, calibrate, communicate
1 rubric
Fixed before you answer. Never rewritten.

How it works

One idea. Six reps.

The same loop learning researchers keep finding works: retrieval, explanation, transfer and feedback. Packed into a quarter of an hour.

  1. 01

    Learn 5 min

    Six swipeable cards: the mechanism, an analogy and where it breaks, real numbers, a quick check.

  2. 02

    Recall 2 min

    The lesson disappears. Write what you remember. Retrieval is what makes it stick.

  3. 03

    Explain 3 min

    Explain it to a smart 15-year-old, in your own words. Short and precise beats long and vague.

  4. 04

    Apply 3 min

    A new situation from a different field that you can only solve if you really get the idea.

  5. 05

    Defend 2 min

    The coach goes after the weakest point in your answers. You hold the line, or learn where it cracks.

  6. 06

    Results 1 min

    Your score, what you nailed, what you missed, and one line worth remembering.

Honest grading

Graded like an examiner. Not a cheerleader.

  • The rubric comes first

    Before you're ever tested on an idea, its definition and core ideas are written down once and never changed. The grader can't move the goalposts after reading your answer.

  • Evidence, not vibes

    Every core idea is marked demonstrated, partial, missing or wrong, with an exact quote from your answer as proof.

  • Numbers come from code

    The model makes structured judgments; the score is calculated from them deterministically. Same judgments, same score.

  • Concise beats long

    Padding doesn't pay. Copying the lesson is detected. Restating the definition when you were asked to apply it scores low.

Explain · graded

Why GPUs run AI

78/100

  • Work splits into independent multiplications

    each multiplication doesn't depend on the others

  • Thousands of simple cores run them in parallel

    a GPU just does them all at once

  • Memory bandwidth limits real speed

    it needs to move lots of data

  • Why a CPU's few fast cores lose here

    No evidence in your answer

Understanding, not memorisationConcision 4/40% copied from lesson

Training modes

Different muscles. Same discipline.

Every mode ends the same way: you have to produce something, and it gets graded.

~15 min

Learn

Learn it, explain it, use it

Study an idea, recall it, explain it simply, then apply it to a new problem.

~15 min

Mental Models

Ways of thinking that travel

Learn a reusable thinking tool, then spot it in two unrelated situations.

~15 min

Argue

Make the best case — both ways

Learn a debate, argue for it, argue against it, then defend your reasoning.

~12 min

Calibrate

Know when you know

Guess first with a confidence level, learn, then see how well-calibrated you were.

~15 min

Communicate

Explain it to anyone

Explain one idea to a child, an adult and a CFO — then in 30 seconds.

~8 min

Review

Keep it sharp

Recall, explain and apply something you learned before — no lesson.

KV cacheHBM memoryTransformersUnit economicsBayes' ruleNetwork effectsLithographyGradient descentDNSOpportunity costBase ratesCAP theorem
Moore's lawPower lawsCompound interestQuantizationTCP handshakePrice elasticitySurvivorship biasAttentionSupply chainsSecond-order effectsRAGLoad balancing

This week

Preview
  1. @ada_codes9 sessions812
  2. @kernel_panic9 sessions745
  3. @marginal_mia8 sessions690
  4. 4@bayes_buddy7 sessions571
  5. 5@you6 sessions503

Weekly leaderboard

A race every week. Trophies that stay.

Every session you finish adds its score to your weekly total. The board resets every Monday. Finish in the top three and a gold, silver or bronze trophy goes into your profile's cabinet for good.

2nd
1st
3rd

One board for everyone. No leagues, no tiers, no pay-to-win.

Learning paths

Follow a path, or let it surprise you.

Guided routes through a whole domain, one generated lesson at a time. Each step knows what came before it.

🧠

How AI actually runs

From GPUs to the economics of AI data centers

10 steps

🔌

From sand to silicon

How chips are made, and why only a few companies can

7 steps

💬

LLMs in practice

What people at work mean when they talk about AI

9 steps

🌐

What happens when you open a website

The invisible systems behind every tap

8 steps

📈

How software businesses make money

The numbers behind tech companies

7 steps

🎲

Thinking with numbers

Know when you know — and when you don't

7 steps

FAQ

Questions, answered.

Why is it invite-only?

Every session runs a real AI model that writes your lesson and grades you against a rubric. We let people in gradually so it stays fast and the leaderboard stays honest. Sign in with Google to request access, and an admin reviews it by hand.

What do you get from my Google account?

Your name and email address, nothing else. No contacts, no Drive, no photos. Your email is never shown to other learners; on the leaderboard you're your username and a generated avatar.

Isn't this just a chatbot?

No. A chatbot agrees with you. Mental Gym runs a fixed loop (learn, recall, explain, apply, defend) and grades each answer against a rubric written before you answered, quoting your own words as evidence. The score is calculated by code from those judgments, not invented by the model.

What will I learn?

AI & Machine Learning, Software & Systems, Computing & Hardware, Business & Strategy, Data & Decisions, Economics & Finance, Science & Engineering. Pick a topic, follow a guided path, or let the curriculum engine choose: it strengthens weak spots, goes one level deeper, or connects ideas you already know.

How does the leaderboard work?

Every session you finish adds its score to your weekly total. Weeks reset Monday 00:00 UTC. The top three each week win a gold, silver or bronze trophy that stays on their profile. One board for everyone: no leagues, no tiers.

Is there an app?

It's a web app built for iPhone first. Open it in Safari, tap Share → Add to Home Screen, and it runs full-screen like a native app. It works on any modern browser too.

Your first rep takes 15 minutes.

Request access with Google. You'll be on the list in seconds, and in the gym as soon as you're approved.