PayKit is an open-source, embedded billing framework for TypeScript applications. It provides a core library (`paykitjs`) that handles subscription management, metered usage tracking, feature entitlements, and webhook processing – all backed by PostgreSQL and currently integrated exclusively with Stripe as the payment provider. The monorepo includes a CLI for project scaffolding and migration, a client SDK, a dashboard plugin (`@paykitjs/dash`), a documentation website (Next.js + Fumadocs), a demo application, and a webhook tunnel worker (Cloudflare Workers + Durable Objects). The architecture is modular: a core `createPayKit()` instance orchestrates services for customers, subscriptions, entitlements, products, and invoices, each following a service pattern with Drizzle ORM models. A plugin system allows custom endpoints, and a provider abstraction (currently only Stripe) handles payment operations. The codebase is well-structured with TypeScript end-to-end, extensive E2E testing against Stripe test clocks, and a clean separation of concerns. However, it is in alpha stage, has duplicated UI component libraries across apps, and is tightly coupled to Stripe – factors that limit immediate reuse without adaptation.