HivePress is an open-source solution for building any type of directory and listing websites, such as business directories, job boards, classifieds, marketplaces, and whatnot.
While it's implemented as a WordPress plugin, it has its own lightweight MVC framework that acts as a wrapper for the WordPress API. This makes extending the core functionality and working with templates, forms, queries, etc. much easier.
The framework docs are organized to resemble the HivePress file structure, so you can easily navigate the code reference and check the implementation while reading the docs.
These docs assume that you are already familiar with the WordPress API and concepts, such as post types, taxonomies, meta boxes, actions, filters, and so on.