PayKit

PayKit is what Better Auth is for authentication, but for payments. An open-source TypeScript library that embeds billing directly into your app. Define plans and features in code, store billing state in your own Postgres, and swap payment providers (Stripe, Polar, Creem) with a single import change.

Still in beta and not yet mature, but the core API is usable. Usage-based billing, feature gating, and webhook handling (with automatic verification and dedup) work today. Worth watching if you want to own your billing layer instead of depending on a hosted service.