Technically it is a plugin for WordPress. Functionally Builderius is a site builder that allows you to create templates for any posts, custom post types, regular pages, archives, “404 error” page, etc. Builderius does not deactivate your theme.
The theme remains active and operational (if you want to put some custom code in functions.php etc). However, since Builderius is a site builder, it allows you to create and display custom templates, which is the “territory” of WP themes.
It makes the process of creating a website convenient and flexible by implementing advanced development techniques. In particular, more granular control over templates and their usage on the site, built-in staging/production modes, full site theme-like export/import, included forms functionality etc. We put a strong emphasis on dynamic data creation and usage inside the templates.
