RAG & Knowledge
second-brain-os
A self-maintaining AI second brain for Obsidian and Claude Code.
★ 888 starsMIT
View guide →Edit RDF knowledge graphs in your browser — no backend needed.
ontosphere is an open-source rag & knowledge project by ThHanke (ThHanke/ontosphere on GitHub). It has 247 GitHub stars and 30 forks, is released under the NOASSERTION license, and was last updated on GitHub on 24 September 2026.
Decide what you want the project to do before installing anything.
Grab the source and skim the README for setup requirements.
Install dependencies and add any API keys or settings it needs.
Launch it and follow the example workflow from the docs.
Exposes its capabilities to AI agents over the Model Context Protocol.
Structures information as a queryable graph.
Bring notes from Obsidian, Notion, and more.
Own your second brain completely.
Combines keyword and semantic retrieval.
Connects notes into a queryable graph.
Download the source and move into the project folder.
git clone https://github.com/ThHanke/ontosphere.git
cd ontospherePull in the Node packages the project needs.
npm installStart the dev server and open the printed URL.
npm run devIt is an open-source project at ThHanke/ontosphere with 30 forks. Check the repo’s contributors and recent commits to judge how active maintenance is.
GitHub does not assert a license for this repo, so treat the code as all rights reserved until the author adds one.
Locally or on your own server, depending on how you deploy it.
Most support OpenAI, Anthropic, Ollama, and other providers via config.
Yes — MCP support lets agents search your knowledge base directly.
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Free and open — grab the source, star the repo, and start creating.