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- Spaced-repetition practice
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Every claim, a source
Learn anything.
And actually remember it.
Type any topic. Nodebook compiles a lesson from real, linked sources, then makes you recall it days later, so it's still there in a month.
- 3 free lessons a month
- No card required
- Reviews scheduled by FSRS
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Why nothing escapes a black holeTeach me
Beginner·Everyday life
02The event horizonDefinitional
PlainExampleMetaphorVisual
What would it actually take to escape a black hole?
Cross this boundary and getting back out would mean travelling faster than light. Nothing can, so the horizon marks the point beyond which no signal returns.
Sources · 4
- Black Holesscience.nasa.gov
- Singularities and Black Holesplato.stanford.edu
- Astronomers Capture First Image of a Black Holeeventhorizontelescope.org
- Event horizonen.wikipedia.org
The receipts
Every sentence has a source. Here's one.
From the lesson “How large language models work”
A large language model takes text, splits it into smaller units called tokens, and predicts a probability distribution for what token should come next.
It generates text by choosing a token, adding it to the context, and repeating the process. It does not retrieve a finished sentence from a hidden book.
Read the whole lesson →Sources · 3
- Vaswani et al. (2017), Attention Is All You Needarxiv.org
- Brown et al. (2020), Language Models are Few-Shot Learnersarxiv.org
- Bender et al. (2021), On the Dangers of Stochastic Parrotsdl.acm.org
Not a badge that says “cited”. The actual links, on the actual lesson.
Why it matters
In a 2025 randomised controlled trial, learners who studied with ChatGPT answered 57.5% of a surprise test correctly 45 days later. Learners who studied without it answered 68.5%.
Barcaui (2025), Social Sciences & Humanities Open 12, 102287
One trial: 120 undergraduates, randomly assigned to two groups (p = .002, Cohen's d = 0.68). Directional, not a law - we link it because we'd want to check it too.
No customer logos here. Nodebook is new and we won't invent them - judge the lesson instead.
See a real lesson →Try one
Three hard topics. Open one and read it.
Not a mock-up and not a video. These are lessons Nodebook compiled, on the page exactly as the app renders them. Press a subject to read its opening - one of them you can listen to.
How it works
Learn. Prove. Refresh.
1
Hand it a topic
Type an idea, an offhand question, or paste a useful link.
Why nothing escapes a black hole
Depth
BeginnerIntermediateProfessional
Explain it through…
Everyday lifeCookingSports
Teach me
2
Learn it clearly
A finite, cited lesson builds intuition before adding precision.
02The event horizonDefinitional
PlainExampleMetaphorVisual
What would it actually take to escape a black hole?
Cross this boundary and getting back out would mean travelling faster than light. Nothing can, so the horizon marks the point beyond which no signal returns.
✓ 4 cited sources·5 concepts
3
Prove what stuck
One short retrieval attempt tells Nodebook what to bring back later.
Recall LockThe event horizon
Why can light not escape past the event horizon?
Escaping would require moving faster than light, which is not possible.
Ideal answer revealedCompare the idea, not the wording.
Got itAlmostMissed
We’ll bring this idea back in 4 days.
The part other tools skip
Reading it is not remembering it.
A lesson you read once is mostly gone inside a week. A few well-timed attempts to recall it are the difference between having read something and knowing it.
With Nodebook’s reviewsRead once
allnone
Day 0Day 7Day 14Day 21
How it bends
Recall it, then be asked again.
Two surfaces do the work. One makes you retrieve the idea from memory instead of re-reading it; the other decides when you see it next, per concept, so the ideas you are shaky on come back and the ones you own leave you alone.
Recall LockThe event horizon
Why can light not escape past the event horizon?
Escaping would require moving faster than light, which is not possible.
Ideal answer revealedCompare the idea, not the wording.
Got itAlmostMissed
We'll bring this idea back in 4 days.
You explain it in your own words first, then reveal and rate what you actually remembered. That rating — not a page view — sets the next review. Explore active recall →
Ready to refresh1 concept
Neural Networks
BackpropagationLast recalled 6 days ago
Refresh this memory →
Nothing else needs your attention right now.
When something is due you get one clear action; when your memory map is stable it stays quiet. Prefer to listen? Any lesson becomes chaptered narration, and Audio Recall puts the same pauses between chapters. Meet Audio Recall →
It compounds
Every lesson becomes a node in your book.
Nothing you compile is spent. Each lesson is broken into concepts, and a concept that turns up in a second lesson doesn’t repeat — it connects. Six subjects stop being six folders and start being one book.
Roman EmpireThe legion
Roman EmpireThe legionMarcus Aurelius
Roman EmpireThe legionNeural networksCross-entropyPhotosynthesisMarcus AureliusVirtue ethicsFrench Revolution
ideas within one lesson the same idea in two subjects
- Concepts
- 38
- Connections
- 60
- Lessons
- 14
- Busiest idea
- 7
“Roman Empire” is doing the most work in this one — it came up in 7 different lessons, which is how the history and the philosophy ended up in the same graph. The library above is an example, not a real person’s. The drawing is not: it is the same layout engine the app runs, over the same shape of data it stores.
And it reads as a shelf, not a folder of documents — every lesson gets a real cover.
Pricing
Start free. Go deep for the price of a coffee.
$11.99/mo
- 30 lessons a month - about one a day
- Scholarly sources - real papers & DOIs
- Full Professional depth
- Chaptered audiobooks with read-along
No ads on either plan - Nodebook doesn't sell them.
Cancel any time from Settings.
Before you sign up
The questions we'd ask.
How is this different from asking ChatGPT?
A chat answers and then forgets you. Nodebook writes a finite lesson from sources you can open, splits it into concepts, and brings each one back for a retrieval attempt days and weeks later. That second half is what decides whether you still know it next month. The full comparison →
Does it make things up?
Lessons are compiled from retrieved material, checked against it, and published with the source list attached. No language model is perfect, which is exactly why the links are on the page: you can open a source and check a sentence yourself instead of trusting us.
What counts as a lesson?
One compiled topic, at whatever depth you pick. Every lesson costs the same, so going deep is never more expensive than skimming. Free includes 3 a month; Pro includes 30.
How long does a compile take?
About 90 seconds. You can close the tab while it works - the lesson is waiting in Learn when you come back.
Can I cancel?
Yes, from Settings, in one tap. Pro keeps working until the end of the period you have already paid for, and nothing you have compiled is taken away afterwards.
Is there an iPhone app?
The web app runs on your phone today, including audio lessons. A native iPhone app is on the way, and this page will say so the moment it ships.
Start
Learn something that lasts.
3 free lessons a month. No card.
iPhone app coming soon.