Multisite allows you to manage multiple websites in a single Magnolia instance. The module extends the Standard Templating Kit. Each site has its own site definition, templates, themes, domains and locales.
The Multisite module is bundled with Magnolia and typically already installed. You can download it from our Nexus repository.
Multisite is an Enterprise Edition Pro module. It is typically already installed. Launch the Configuration app and go to
/modules/extended-templating-kit to check.