hutch is a small program that takes a config.json file and spins up a proxy server that takes care of all your sites. It uses seaport to manage your ports automatically, and http-proxy to proxy all your requests to various servers. Because seaport uses semvers, you can place different versions and roles of the same server in your config.json without having to worry about port numbers.
The real magic is seaport and http-proxy. hutch just allows you to use them together.