Hi there,
documentation.generatepress was custom coded by Tom for that very purpose. You could do something similar, just using Posts. Adding functionality such as the contextual Sidebar menus could be done with a plugin, e.g:
https://wordpress.org/plugins/advanced-sidebar-menu/
Creating a footer menu to display Featured links could be done with Tom’s own WP Show Posts:
https://wordpress.org/plugins/wp-show-posts/
The rest would be simple formatting that could be done via the customiser.