Helen Hou-Sandi

Really Simple Gallery Widget adds a widget to display images from the Media Library, no extra uploading or creating custom post types required. You can choose to show images from a specific post/page, the entire media library, or a specific set of attachment IDs. On single pages/posts, you can also show only images attached to the item currently being viewed. Especially helpful if your galleries are based on what’s attached to a post and you want to be able to easily display those images in a widget area.
<h4>Features</h4>
<ul>
<li>Add as many widgets as you want, wherever you want</li>
<li>Display images from a specific post/page, the entire Media Library, or a specific set of attachment IDs</li>
<li>Display images from the post/page currently being viewed</li>
<li>Select a number of images</li>
<li>Select any registered size in WordPress</li>
<li>Display the images in various orders</li>
<li>Show or hide captions</li>
<li>Link the images to the original file, post, anchor in the post, attachment page, or nothing. NOTE: If the image is not attached to a post, the file link will be used instead of the post or anchor in the post.</li>
<li>Add a prefix to the link and image title (appears as a tooltip)</li>
<li>Use a rel attribute for the link – great for lightboxes</li>
</ul>

Really Simple Gallery Widget

Simple widget for displaying images from the Media Library with plenty of configurable options.

zackdesign

RSS Image Widget fetches images from any RSS/Atom feed that uses enclosures and displays them in a responsive grid with a built-in lightbox. Works as both a classic widget and a Gutenberg block.
Features:
<ul>
<li>Widget + Block — Use in sidebars (classic widget) or anywhere in the block editor</li>
<li>Lightweight — No jQuery, no external CDN. Just a tiny vanilla JS lightbox (~2 KB)</li>
<li>Responsive grid — CSS Grid layout adapts to any container width</li>
<li>Lazy loading — Images use native browser lazy loading</li>
<li>Accessible — Lightbox supports keyboard navigation (Escape to close)</li>
<li>Zero configuration — Just add a feed URL and go</li>
</ul>
Upgrading from v2.x:
The Bootstrap classes (<code>row</code>, <code>col-xs-12</code>) and external Lightbox2 CDN have been replaced with clean semantic HTML, a responsive CSS Grid layout, and a bundled vanilla JS lightbox. If you had custom CSS targeting the old classes, you will need to update it to use the new <code>.rss-image-gallery</code> BEM classes.

RSS Image Widget

Display images from an RSS or Atom feed as a widget or block with a lightweight lightbox gallery.

Really Simple Gallery Widget vs RSS Image Widget