Threads displays a timeline of related posts.
The architecture of Threads is a custom taxonomy coupled with a "dependent" custom post type where content (description, featured image, etc.) for the taxonomy term can be stored. The CF Taxonomy Post Type Binding plugin provides the functionality to keep the post type and taxonomy term in sync with each other. The thread display is the display of the custom post type, while the taxonomy is not public.
Threads separates presentation files into views, with appropriate filters on each. You can override the templates, CSS, etc. used to display a thread timeline by using these filters.
Developement for Threads occurs in the public GitHub repository, please collaborate with us there.