Koa aims to be a smaller, more expressive, and more robust foundation for web applications and APIs. Through leveraging generators Koa allows you to ditch callbacks and greatly increase error-handling. Koa does not bundle any middleware.
A Node.js web service framework optimized for building semantically correct RESTful web services ready for production use at scale. it optimizes for introspection and performance.
Go is expressive, concise, clean, and efficient. Its concurrency mechanisms make it easy to write programs that get the most out of multicore and networked machines, while its novel type system enables flexible and modular program construction. Go compiles quickly to machine code yet has the convenience of garbage collection and the power of run-time reflection. It's a fast, statically typed, compiled language that feels like a dynamically typed, interpreted language.
Express is a minimal and flexible node.js web application framework, providing a robust set of features for building single and multi-page, and hybrid web applications.
Under the hood, Nest makes use of Express, but also, provides compatibility with a wide range of other libraries, like e.g. Fastify, allowing for easy use of the myriad third-party plugins which are available.