Apple used to have a fantastic application called OSX Server (now called MacOS Server) which allowed you to run a full server from any OSX computer. A server can  allow you share files, run your own email or web server, remotely connect in to your office etc.  OSX server was particularly powerful running on a Mac Mini. With OSX Mojave 10.14 Apple killed off OSX server, but it is still possible to download an older version from Apple that still works. You need need to purchase OSX server on a newer Mac running Catalina, then go to an older Mac signed in using the same Apple ID and grab the older version of Server from the Purchase history.

Here’s how.