NestJS

NestJS brings structure to backend TypeScript with dependency injection, modules, guards, and interceptors. Basically, Angular's architecture applied to the server side.

Everything is free under MIT. The framework, CLI, all modules (GraphQL, WebSockets, microservices, CQRS), all open source. NestJS makes money through enterprise support and training, not feature gating.

The catch: the learning curve is real. If you're coming from Express, the decorators, dependency injection, and module system feel over-engineered for simple APIs. NestJS shines when your API has 50+ endpoints with complex business logic. For a simple CRUD API, it's a cannon for a mosquito. And the decorator-heavy style means your code is deeply coupled to NestJS conventions. Migrating away is not trivial.