Nx
Monorepo toolchain — Nrwl, 2018 (Victor Savkin, Jeff Cross, ex-Angular team). Focus: smart build cache, affected-test detection, plugin-based workflows.
Built on targets (compile, test, lint) that run over a dependency graph. Nx Cloud (commercial) provides distributed cache + replay. Plugins for Angular, React, Next, Vue, Node, Nest, Express, Storybook, Cypress.
Competitor: Turborepo (lighter, more JS-focused), Bazel (more correct but steeper), Lerna (now maintained by the Nx team). Nx wins in larger polyglot frontend monorepos.