Koa

Koa is a web framework for Node.js that provides a minimal foundation for building web applications and APIs. Developers use it to create servers with middleware functions composed in a stack-like manner. The framework emphasizes async functions to handle asynchronous operations, allowing developers to avoid callbacks and improve error handling. Koa does not include bundled middleware in its core, instead offering a set of methods for common tasks like content negotiation, caching, and redirects while maintaining a small footprint.

Koa was developed by koajs and is distributed under the MIT license. The framework is designed to be more expressive and robust than similar tools, with middleware that cascades in a traditional way through upstream and downstream execution patterns. Developers can write middleware using async and await syntax to suspend execution and pass control between middleware functions in a clear, readable manner.