dune

Dune's composable build system allows multiple projects to be combined into a single build, simplifying development on multiple packages and enabling monorepos as highlighted in the README.

It correctly handles multi-package repositories by using installed libraries via opam, even when they exist in the source tree, avoiding version conflicts through commands like 'dune build --only-packages'.

Dune can build against several configurations at once, making it easy to maintain packages across different OCaml versions and handle cross-compilation, as noted in the multi-configuration building section.

With minimal overhead, parallel builds on all platforms, and no system dependencies beyond OCaml, Dune is highly performant and portable, even on Windows via binary installers.