Zensical Spark is our offering for professional users. In the past 12 months, we've had numerous conversations with organizations and enterprises to understand how they adapted Material for MkDocs to their processes and workflows. Our goal with Zensical is to build a far more flexible solution than (Material for) MkDocs, developed closely alongside the professional users who rely on it daily. This is a paid product and represents the way we ensure the long-term sustainability of the project.
Zensical itself is entirely free OSS software.