This is really interesting. I haven't tried it, but it's definitely a new approach to designing WordPress themes (as far as I know).

Ok, I've got ask. Why isn't pinegrow.com built on WordPress?

It's built with Pinegrow as a static HTML page, with documentation part done with Jekyll. For some sites static HTML works better than CMS.

But the plan is that we soon transition to WP because we need more flexible documentation / support section with tags, categories and multiple users.