GalaxyBrain is a local-first knowledge system where pages have variables, formulas, and live references between them. Define a value on one page, reference it from another, and it stays in sync automatically. Like a programming environment crossed with a document editor. Everything is stored as structured JSON files on your machine. There's a built-in HTTP API and MCP tool so you can point Claude Code, Codex, or a local model at the same folder and build on top of it. No account needed.