How to do it...

We will use multisites in Drupal 8 by two subdomains under localhost:

1. Copy sites/example.sites.php to sites/sites.php.
2. Create a dev1.localhost and dev2.localhost folder inside the sites folder.
3. Copy the sites/default/default.settings.php file into dev1.localhost and dev2.localhost as settings.php in their respective folder:

1. Got to dev1.localhost and run the installation wizard.
2. Got to dev2.localhost and verify that you still have the option to install a site!