Dune is a build system designed for OCaml/Reason projects only. It focuses on providing the user with a consistent experience and takes care of most of the low-level details of OCaml compilation. All you have to do is provide a description of your project and Dune will do the rest.
The scheme it implements is inspired from the one used inside Jane Street and adapted to the open source world. It has matured over a long time and is used daily by hundred of developers, which means that it is highly tested and productive.