From what I can make out:

1. Define all document types (document metadata and structure) in their custom JSON.

2. They build pretty looking CRUD forms based off the JSON so non technical content writers can fill in and manage content.

3. Expose all documents via a REST API with a bespoke query language.

4. Allow content to be edited collaboratively and changes to be scheduled / buffered.

That's about it, actually. Would work very well when I build a site for my mum's chocolate shop.