plainware

Signteer is a lightweight volunteer sign-up sheets plugin designed to help your organization keep track of volunteer opportunities, tasks and sign-ups.
Features:
<ul>
<li>Admins can post sign-up sheets with permalinks.</li>
<li>Volunteers can sign up directly from the sheet page.</li>
<li>Admins can control the tasks for each sign-up sheet and number of spots for each task.</li>
<li>Admins can view the list of all volunteers with the history of their involvement.</li>
</ul>
<h3>Support</h3>
Please contact us at https://www.signteer.com/
Author: Plainware 
Author URI: https://www.signteer.com

Signteer

A volunteer sign-up sheets plugin to let your volunteers sign up for your tasks.

Andrew Norcross

Liquid Web

Allow customers to opt-in to news and information about the individual 
products they purchase. Each signup is listed in the admin dashboard, 
and actions and filters exist to hook into various email marketing provider.
Features
<ul>
<li>CSS based countdown display</li>
<li>available actions and filters to modify functionality.</li>
</ul>

WooCommerce Interest In Products

Allow customers to opt-in to notices about individual products.

Signteer vs WooCommerce Interest In Products