Yoren Chang

Thanks to <a href="https://github.com/WebDevStudios/Taxonomy_Single_Term" rel="nofollow ugc">Taxonomy_Single_Term</a>, a library created by <a href="http://webdevstudios.com/" rel="nofollow ugc">WebDevStudios</a>, it made my work much easier on creating this plugin.
With Categories Metabox Enhanced, you can:
<ul>
<li>Change the built-in Categories metabox/panel to a single term UI, which means replacing the checkboxes with radio buttons or a select drop-down.</li>
<li>Apply the single term UI to other hierarchical taxonomies in the plugin’s Settings page.</li>
<li>Customized the single term UI by setting these options:
<ul>
<li>Priority and position of the metabox placement.</li>
<li>Title of the metabox.</li>
<li>If child-terms should be indenting.</li>
<li>If adding of new terms from the metabox is enable.</li>
</ul>
</li>
</ul>

Categories Metabox Enhanced

Replace the checkboxes with radio buttons or a select drop-down in the built-in Categories metabox and Gutenberg sidebar panel.

Tahir Yasin

This plugin adds a meta box to upload multiple images for posts and pages. You can enable it for custom post types also, please see installation instructions.
<h3>miu_get_images()</h3>
This function can be called from any template file to get attached images for the page/post being viewed. 
It returns an array of the attached image URL.
It take only one argument:
<ol>
<li>
post_id (integer) to get images linked to a specific post
 http://www.example.com/image-1.png 
 [1] => http://www.example.com/image-2.png 
)
?></li>
</ol>

Multi Image Upload

This plugin adds a meta box to upload multiple images for posts and pages.

Categories Metabox Enhanced vs Multi Image Upload