John Regan

This plugin adds a simple button to the post editor screen which allows editors to duplicate posts quickly and easily. It’s so simple that no configuration is necessary!
Features
<ul>
<li>Copies with just one click!</li>
<li>Make duplicates from the List or Edit Post view</li>
<li>No configuration needed</li>
<li>Works for all Post Types</li>
<li>Integrates seamlessly with the WordPress UI</li>
<li>Extremely lightweight (~8KB)</li>
<li>Thorough Documentation</li>
</ul>

Simple Copy Post Button

Copies/Duplicates Posts, Pages, and Custom Post Types with just one click.

Dhanendran Rajagopal

Initial version of this plugin is a fork of https://wordpress.org/plugins/taxonomy-converter/.
Copy or convert terms between taxonomies.
Taxonomies include categories, tags and any other custom taxonomies that may be present with your active theme and plugins.
This plugin, allows you to copy (duplicate) or convert (move) terms from one taxonomy to another or to multiple taxonomies, while maintaining associated posts.

Term Taxonomy Converter

Copy or convert terms between taxonomies.

Simple Copy Post Button vs Term Taxonomy Converter