Drupal Multisite enables separate, independent sites to be served from a single codebase.
Drupal is a free and open-source web content management framework.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
Internet Information Services (IIS) is an extensible web server software created by Microsoft for use with the Windows NT family.
PHP is a general-purpose scripting language used for web development.