Justin Tadlock

Hybrid Hook is a plugin that allows end users the ability to tap into the <a href="https://wordpress.org/extend/themes/hybrid" title="Hybrid WordPress theme framework" rel="ugc">Hybrid theme’s</a> extensive hook selection by providing a user interface in the WordPress admin for adding custom content.
You must be using at least version 0.9 of the <a href="https://wordpress.org/extend/themes/hybrid" title="Hybrid theme" rel="ugc">Hybrid theme</a> for this plugin to work. It will also not work with any other themes.
Features:
<ul>
<li>Ability to add custom HTML nearly anywhere on your site.</li>
<li>Use shortcodes to quickly add content.</li>
<li>Allows the input of JavaScript.</li>
<li>User can select the priority the code will run.</li>
<li>Can execute PHP code if the option is selected.</li>
</ul>

Hybrid Hook

Allows the addition of HTML, shortcodes, PHP, and/or JavaScript to the Hybrid theme's hooks from the WordPress admin.

Stephen AfamO

This plugin allows you to use any HTML or PHP file as the template for any page or post.
Simply upload the file and select it. 
You can upload custom js and css files into the media library and link to them from the HTML file.
Options:
<ul>
<li>Overwrite All: You overwrite the entire theme and use your custom file</li>
<li>Overwrite Content: Keeps the header, footer, sidebar, e.t.c. Simply overwrites the body of the page or post</li>
<li>Above Content: Your custom content is simply added to the top of the page content</li>
<li>Below Content: You custom content is placed just beneath the page content.</li>
</ul>
<h4>Adding support for custom post types</h4>
By default the pulugin works with pages and posts, however, go to the settings to enable it on any other registered post type.
use the <code>hppp_post_types</code> filter to add more post types.
Like this:
<pre><code> public function post_type_modify ($post_types) {
 $post_types[] = 'custom_post_type';
 return $post_types;
 }

 add_filter( 'hppp_post_types', 'post_type_modify' );
</code></pre>

Custom HTML/PHP Post Templates

I use this on a couple sites I own and it works wonderfully.
I hope you can find it useful. 

Works like a charm

Use your HTML or PHP files for any page or post.

Hybrid Hook vs Custom HTML/PHP Post Templates