GalaxyBrain is a programmable knowledge system that runs entirely in the browser as a single HTML file, with no account or server required. Each page can define custom variables that act as live metadata — reference them from any other page and every connected value updates in real time when you change the source. It behaves like a lightweight scripting environment embedded in a document editor: useful for tracking project specs, config values, research parameters, or any structured information that needs to stay in sync across multiple notes.
All data is stored locally as plain JSON files, so you own everything and can process it with any tool. A built-in HTTP API and an MCP server mean you can drive the app programmatically — point Claude Code, Codex, or a local model at the same folder and build workflows on top of your notes without leaving the system. The single-file distribution makes it trivial to run offline or self-host. It's a good fit for developers, researchers, and power users who want a knowledge base they can actually extend and automate rather than just write in.