How to set up WordPress in the intranet?

I recommend (and use myself) XAMPP located here LINK, which will allow you to run a web-server on a machine of choice.

Once you setup XAMPP, you would install WordPress or WordPress with Multisite (enabled) just like you would any other WordPress installation on a website host.

You have full control over your server (run out of a folder of choice) and you also have full control over the MySQL server for which you need to create a database/username/password to give to WordPress during the setup process.

If you plan on having a machine that is always on then that’s your best solution. I use and countless others do to, for local development.

XAMPP also comes with a handy control panel that sits in your system tray for which to control the server (start/stop Apache and MySQL);

XAMPP Control Panel Application