Mandatory

Mandatory is an installation profile for Drupal 8/9, allowing Drupal to be installed without ANY optional components (modules, themes). So you'll end up with an initial Drupal installation where only mandatory components are enabled, which are basically the modules System and User, and the Stark theme.

To use it, download Drupal 8/9 and this profile, start the installation process and select 'Mandatory' as installation profile. If you're using Composer follow these steps:

composer create-project drupal/recommended-project some-dir
cd some-dir
composer require drupal/mandatory

Now you can start the installation as usual, maybe using Drush or Drupal Console:

drush si (for Drush)
drupal si (for Drupal Console)

Beware, your site will look rather ugly, as Stark will be set as default theme. And there won't be a menu, so you'll have to navigate through the site using internal paths, like 'admin/modules' - until you enable some core or custom modules to make your site shiny again.

What's the use case?

Basically with this distribution you don't need to disable any optional dependencies after installation. Let's say you're building a REST backend based solely on custom coded entities using only base properties. Why should you bother with uninstalling unused modules like Node, Taxonomy, Menu, Field UI and others? This distribution is a good way to "start from scratch".

How to try it out quickly?

You can give it a try on simplytest.me. User / Password: admin

What's the difference to the Minimal installation profile?

The Minimal installation profile delivers an opiniated set of minimal dependencies (enabled modules and themes), e.g. Node, Block, Menu, DB Log, Field or Page Cache. You'd need to uninstall them all to achieve the same effect.

Why not simply use an empty profile, without dependencies?

Despite having no dependencies specified in your info.yml file, Drupal will still enable some modules by default, e.g. Field, File or Update. What Mandatory does is disabling those leftover modules.