Drupal Multisite enables separate, independent sites to be served from a single codebase.
Drupal is a free and open-source web content management framework.
Facebook pixel is an analytics tool that allows you to measure the effectiveness of your advertising.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Sendinblue is an email marketing solution for small and medium-sized businesses that want to send and automate email marketing campaigns.
Varnish is a reverse caching proxy.