Second Neuron by Swapnil

Second Neuron turns the articles you read into a personal knowledge graph that actually sticks.
Click the toolbar icon on any page — a docs article, a blog post, a paper. The extension extracts the main content locally, sends it to your private
Second Neuron account, and Claude identifies the concepts worth remembering and links them into your existing graph. Later, spaced repetition surfaces those concepts at the right moment through flashcards, Feynman-style explanations, code challenges, and concept-connection reviews.

What you get

• One-click capture from any page (uses Mozilla's Readability to pull clean article text).
• Concepts automatically classified, summarized, and linked — no manual tagging.
• Review queue based on the FSRS algorithm — the same scheduling used by modern Anki forks.
• Multiple review modes: flashcards, Feynman explanations, short code challenges, connection tests.
• Your data stays in your account. No analytics, no ads, no model training on your captures.

Setup

1. Sign in at secondneuron.com.
2. Open Settings → API Keys and generate a key (starts with sb_).
3. Paste the key into the extension's settings page. Done.
   Open source. Privacy policy: https://secondneuron.com/privacy