Nx is a build system for JavaScript and TypeScript monorepos, made by the company Nrwl; plugins extend it to other languages such as Java and .NET. A monorepo is one code repository that holds many projects, for example a front end, a back end and shared libraries. Nx keeps builds and tests fast as such a repository grows.
Nx reads the workspace and builds a project graph and a task graph that show how the projects depend on each other. It runs tasks such as build, test and lint in the right order, in parallel where possible, and caches their results so that unchanged code is not rebuilt. Affected commands run only the tasks that a change touches. Module boundary rules block unwanted dependencies between projects, and plugins for React, Angular, Next.js, Nest and other tools generate code and configure tasks.
Nx itself is open source under the MIT license. Nx Cloud, the company's paid service, adds remote caching, distributed task execution across CI machines and self-healing CI; it has a free Hobby plan and usage-based Team and Enterprise plans.