The Openstad frontend is built upon the ApostropheCMS, there are also a few react application that are run as modules inside ApostropheCMS.
The CMS is mostly a tool to create a website around the OpenStad tools. We are not quite there yet, but eventually the tools should be available as components. All OpenStad information should be stored through the API in theMySQL database. The CMS data is stired in the frontend Mongo DB.
Some standard functionality is available in the Apostrophe framework, but not or hardly used because it is also provided in teh OpenStad tools. For example caching and tagging of content.