Dune is a composable build system and package manager for OCaml and related languages. In production, it parses `dune`/`dune-project`/`dune-workspace` configuration files, generates build rules for libraries, executables, foreign stubs, tests, documentation, and integrations (Melange, js_of_ocaml, wasm_of_ocaml, Rocq/Coq, ctypes, menhir, mdx), then executes those rules with an incremental engine featuring memoization, file watching, sandboxing, caching, promotion, and an RPC-accessible watch mode. The main entry point is the `dune` CLI (`bin/main.ml`), with subcommands grouped under `bin/`: `build`, `exec`, `runtest`, `fmt`, `promote`, `describe`, `pkg`, `trace`, `rpc`, `ocaml`, and `rocq`. Dune also includes an experimental package manager (`dune pkg`) that solves opam dependency formulas, fetches sources, and writes lock directories.