Niraj Chauhan

This plugin will help the user to add a drop-down-custom-taxonomy box with the help of small code on his desired location.
<h4>Options</h4>
just place this small code into your theme file and the drop-down box will appear on that page 
code: 
for example, if you want to display it on home page, 
then navigate to index.php, the inside that put this code, if you want to display the custom taxonomies, then just replace category with your custom taxonomy name.

Drop-down-taxonomy

This plugin will help the user to add a drop-down-custom-taxonomy box with the help of small code on his desired location.

Mats Westholm

Add one or more Custom Taxonomy to your wordpress managed website.
This plugin is focused on an easy to use interface with small number of choices to make it easier to use for a non technical user.
MW Taxonomy let you choose
<ol>
<li>Taxonomy name in plural and singular,</li>
<li>slug</li>
<li>select the post types (default and custom) where your custom taxonomy can be used</li>
<li>select wheather it should be hierarchical or not</li>
<li>select wherher the taxonomy should be indexed by search engins or not</li>
</ol>
MW Taxonomy includes a widget Custom Taxonomy List for presenting taxonomies in the blog. You need to use a theme that supports widgets for this, that is a classic (non-block) theme. Use the plugin <a href="https://wordpress.org/plugins/classic-widgets/" rel="ugc">Classic Widgets</a> if you don’t find the widget.
Taxonomies can also be presented by Tag Cloud widget or menus (classic theme).
Works in multisite environment as well.
<h4>Docs & Support</h4>
Please ask support questions in the plugin [support forum].(https://wordpress.org/support/plugin/mw-taxonomy)

MW Taxonomy

Easy to use wordpress plugin to add a custom taxonomy

Drop-down-taxonomy vs MW Taxonomy