Hemant Jangir

Back In Stock Notifications allows your WooCommerce store to:
<ul>
<li>Notify customers when out-of-stock products are available again.</li>
<li>Enable a waitlist for sold-out products.</li>
<li>Support double opt-in email confirmation.</li>
<li>Automatically send back-in-stock notifications.</li>
<li>Let logged-in users manage their alerts from the “My Account” page.</li>
<li>Include a simple shortcode to place subscription forms anywhere on your site.</li>
</ul>
This plugin is fully compatible with WooCommerce and supports variable products and backorders.
<h3>Additional Notes</h3>
<ul>
<li>Works only with WooCommerce installed and active.</li>
<li>Emails are sent via WooCommerce mailer.</li>
<li>All subscriber data is stored in a custom database table.</li>
</ul>

Back In Stock Notifications

Notify customers when your products are restocked.

Freemius

Tom Ford

Unofficial addon for Ninja Forms. 
This gives you a few features to conditionaly highlight fields in the submission email received from Ninja Forms. 
This is done for now based on keywords found in the questions or in the replies or a combination. 
It can also automatically give numbers to the fields.
More features are coming. Please use the donate button to support and motivate.

Back In Stock Notifications vs Tweaker for Ninja Foms emails