This project is of particular interest because it currently (08/04/2021) has three incarnations on different sites.
The functionality is simple: Allow site-owners to upload files (usually PDFs but also others, such as images, Word documents or Power Point presentations) to a document library, giving them custom titles, images, categories and other terms. Not only uploaded files can be added, however; any URL can also be added as a document, allowing a very flexible system.
A frontend view is also available for visitors to browse the library, search by title and filter by any taxonomy terms.
In each incarnation the main difference has been that the taxonomies have needed to be customised to fit the site-owner’s needs.
The solution is provided as a WordPress plugin that gives the site-owner a shortcode to output the frontend of the library anywhere they like. Users can search and filter the documents as described and switch between a grid or a tabular presentation.
The fact that this functionality has been used on a number of sites means that I have had more opportunity than normal to refine the code; as well as the impetus to modify the way the plugin is set up in order to allow it to be more readily adapted to different requirements.
An early version of this plugin can be seen running at https://www.youth.ie/documents/ – the other two instances are behind access-restricted login requirements.