Sonnet includes WPBakery Page Builder by wpbakery. You can use WPBakery Page Builder inside Sonnet for free. Please note that it is not a freeware though. You can not use it apart from Sonnet unless you purchase the appropriate license.

Sonnet supports WPBakery Page Builder built-in content elements, as well as unique Sonnet content elements – simply click the “by Sonnet” link in content elements categories filter.