Simon Wheatley

Provides a drop-down to select different templates for posts from the post edit screen. The templates are defined similarly to page templates, and will replace single.php for the specified post. This plugin will NOT switch the templates for the different posts in a listing page, e.g. a date or category archive, it will only affect the template used for single posts (i.e. you can choose a template which is not single.php).
Post templates, as far as this plugin is concerned, are configured similarly to <a href="https://codex.wordpress.org/Pages#Creating_Your_Own_Page_Templates" rel="nofollow ugc">page templates</a> in that they have a particular style of PHP comment at the top of them. Each post template must contain the following, or similar, at the top:
<pre><code><?php
/*
Template Name Posts: Snarfer
*/
?>
</code></pre>
First note: Page templates use “Template Name:“, whereas post templates use “Template Name Posts:“.
Second note: You must have the custom post template files in your theme in the same directory/folder as your index.php template file, not in a sub-directory/sub-folder.
<h3>Developers</h3>
If you want to implement the custom post templates on a custom post type, you can use the <code>cpt_post_types</code> filter, here’s an example below of adding the custom post template selector and metabox to the “Movie” and “Actor” custom post types. This code can be added to a plugin or to the <code>functions.php</code> file in your theme.
<pre><code>/**
 * Hooks the WP cpt_post_types filter 
 *
 * @param array $post_types An array of post type names that the templates be used by
 * @return array The array of post type names that the templates be used by
 **/
function my_cpt_post_types( $post_types ) {
 $post_types[] = 'movie';
 $post_types[] = 'actor';
 return $post_types;
}
add_filter( 'cpt_post_types', 'my_cpt_post_types' );
</code></pre>

Custom Post Template

Provides a drop-down to select different templates for posts from the post edit screen. The templates replace single.php for the specified post.

Matt Martz

Prints an html comment in the footer of every page letting you know which template file of your theme was used for the display.
This plugin is aimed towards theme developers and for theme support. It is recommended to only have this plugin activated during development or support as it will expose your file system path structure.
Props to <a href="http://flushinc.com/" rel="nofollow ugc">Joel Fisher</a> for the idea behind this plugin.
<h3>Upgrade</h3>
<ol>
<li>Use the plugin updater in WordPress or…</li>
<li>Delete the previous <code>show-template</code> folder from the <code>/wp-content/plugins/</code> directory</li>
<li>Upload the new <code>show-template</code> folder to the <code>/wp-content/plugins/</code> directory</li>
</ol>
<h3>Usage</h3>
<ol>
<li>Install and activate.</li>
<li>View source of your blog through your web browser. You will see a html comment in the form of <code></code></li>
</ol>

Show Template

Prints an html comment in the footer of every page letting you know which template file of your theme was used for the display.

Custom Post Template vs Show Template