Apache is a free and open-source cross-platform web server software.
Backdrop is an open-source content management system (CMS) derived from Drupal 7, offering a user-friendly interface, customisable content types, taxonomies, views, theming capabilities, extensibility through modules, and regular security updates.
PHP is a general-purpose scripting language used for web development.
Progressive Web Apps (PWAs) are web apps built and enhanced with modern APIs to deliver enhanced capabilities, reliability, and installability while reaching anyone, anywhere, on any device, all with a single codebase.
Varnish is a reverse caching proxy.