utcwebdesign

Simple-Custo-taxo (Simple Custom Taxonomy) is a simple (as the name suggests) plugin that adds an extra taxonomy option for your posts and can be added to your site by adding the widget to your sidebar.
Simply create categories in the ?custom categories? section that will now appear in your Posts main menu and add posts to that category as you normally would. The widget then creates an unordered list of your custom taxonomies. Simple.
For more information go to <a href="http://www.utcwebdesign.co.uk/blog/development/instructions/simple-custo-taxo-wordpress-plugin" rel="nofollow ugc">http://www.utcwebdesign.co.uk/blog/development/instructions/simple-custo-taxo-wordpress-plugin</a>

Simple-Custo-Taxo (Simple Custom Taxonomy)

Adds an extra taxonomy option for your posts and add to your site by using the widget in your sidebar.

HelgaTheViking

Replace the default taxonomy boxes with a custom metabox that uses radio buttons… effectively limiting each post to a single term in that taxonomy.
A plugin options page allows the user can select which taxonomies she’d like to switch to using the custom radio-button style metabox.
Originally based on the the <a href="https://github.com/stephenh1988/Radio-Buttons-for-Taxonomies" rel="nofollow ugc">class by Stephen Harris</a>
<h4>Support</h4>
Support is handled in the <a href="https://wordpress.org/support/plugin/radio-buttons-for-taxonomies" rel="ugc">WordPress forums</a>. Please note that support is limited and does not cover any custom implementation of the plugin. Before posting a question, read the <a href="https://wordpress.org/plugins/radio-buttons-for-taxonomies/#faq" rel="ugc">FAQ</a> and confirm that the problem still exists with a default theme and with all other plugins disabled.
Please report any bugs, errors, warnings, code problems to <a href="https://github.com/helgatheviking/Radio-Buttons-for-Taxonomies/issues" rel="nofollow ugc">Github</a>

Radio Buttons for Taxonomies

Thank you so much for this plugin, so easy to use and makes creating a single category situations much easier.

Oh this is a life saver!

JUST WORKS

Many thanks to the author for this great plugin. Does one things and does it very well. Works with classic editor and block editor.

5 stars is not enough. Works with Gutenberg

We've been using this plugin for longer than we can remember, never had any issues whatsoever, highly recommended!

Excellent

Replace the default taxonomy boxes with a custom metabox that uses radio buttons... effectively limiting each post to a single term in that taxonomy.

Simple-Custo-Taxo (Simple Custom Taxonomy) vs Radio Buttons for Taxonomies