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Automattic/wp-calypso
The JavaScript and API powered WordPress.com
Calypso is the actual React/Redux frontend that powers WordPress.com — the dashboard, reader, and most logged-in surfaces. It's a production monorepo at real scale, not a reference implementation. Useful if you're studying how a large TypeScript/React SPA is structured at a company that has been running one for a decade.
The codebase reflects real decisions made under real constraints: you can see how they've structured a monorepo with dozens of apps sharing packages without collapsing into a big ball of mud. The ongoing Redux-to-React-Query migration (documented in .claude/skills/) is a live case study in how you incrementally extract state management from a massive existing codebase. CI is genuinely sophisticated — TeamCity for branch builds, Buildkite for desktop artifacts, GitHub Actions for PR automation, and Playwright e2e with AI-assisted test healing. The Claude agent configuration for test generation and healing is an interesting real-world example of integrating AI tooling into an existing engineering workflow.
Getting it running locally requires editing your hosts file and understanding which of the several Dockerfiles, Vagrantfiles, and yarn workspaces is relevant to what you're trying to do — the README makes it look simple, but it isn't. The Redux layer is everywhere and the React Query migration is in progress, meaning you'll encounter both patterns simultaneously with no clear signal on which is authoritative for a given slice of state. The GPL v2 license means you can't use extracted pieces in proprietary projects without contamination concerns. And the repo is so large and so tightly coupled to WordPress.com infrastructure (feature flags, A/B experiments, internal APIs) that contributing meaningfully requires weeks of context-building before your first useful PR.