Ooypunk

Once upon a time there was a website in the auld style, with imagery in an images directory. But then it was said that 
the website should be built anew, but in WordPress, and the images were transported by FTP to the new structure. But 
the new pages and posts needed images, but the images were not in the Library. 
This plugin scans the upload directory for images that are not yet in the Library, and provides links for each one to 
be included.

CIT Media Sync

Plugin to add files to the Media Library that were previously uploaded by FTP.

Marco Milesi

WP Attachments enhances the download experience and file management in WordPress. It automatically displays attachments in your posts and pages, so you don’t need to manually insert download links. 
Easily attach, unattach, or reattach files directly from the media library.
Key Features: 
– 🤖 Automatically displays attachments after post content 
– ℹ️ Backend metabox for managing attachments 
– 🔃 Quick Attach, Unattach, and Reattach actions in the Media Library 
– 🔢 Download counter with anti-spam and logged-in user filtering 
– 🧑‍💻 Developer hooks and filters for customization 
– 🛍️ WooCommerce compatible 
– 🎨 Five icon packs to choose from 
– 📜 Supports posts, pages, and custom post types 
– 🎢 Customizable themes (title, date, size, caption, and more)
<a href="https://www.youtube.com/watch?v=J7gf0hxl_z8" rel="nofollow ugc">Video Overview</a>
<h3>Contributions</h3>
<ul>
<li>Part of <a href="http://www.wpgov.it" rel="nofollow ugc">WPGov.it</a>, providing open source solutions for Italian Public Government websites.</li>
<li>Thanks to the Italian community <a href="http://www.porteapertesulweb.it" rel="nofollow ugc">Porte Aperte sul Web</a> for beta testing and ideas.</li>
<li>Metabox based on <a href="https://wordpress.org/plugins/ij-post-attachments/" rel="ugc">IJ Post Attachments</a></li>
<li>Some icons by <a href="http://p.yusukekamiyamane.com/" rel="nofollow ugc">Yusuke Kamiyamane</a>.</li>
</ul>

WP Attachments

Nice and useful plugin. The only downside is that it lacks a setting to show image thumbnails instead of a generic image icon in the edit metabox.

Show thumbnails instead of icons in metabox

A powerful solution to manage and display your WordPress media attachments in posts and pages.

CIT Media Sync vs WP Attachments