brockangelo

This plugin schedules a daily event using wp_cron that deletes all comments marked “spam” in the database, then optimizes the comments table.
Brief reason why I made such a low-tech plugin:
Akismet catches all the spam, but when I was looking at the size of my backups one day, 
I noticed that there were large numbers of comment spam across several sites that were undeleted and they 
made the databases fairly large. So I setup a cron job on my server that deletes the spam.
Since I had never written a plugin, I thought this might be helpful for those who do not have 
a dedicated server, shell access to their site, or the knowledge of (or interest in ) cron to set this up.
Spam is not deleted until you start the schedule after the plugin is activated. I created buttons 
to start and stop the schedule if you need that layer of control. There is also a button for deleting all spam manually.

Delete Spam Daily

Uses wp_cron to delete comments each day that are marked "spam" in the database.

Scott Kingsley Clark

Requires PHP 5.6+ and WordPress 4.9+
Create and Manage Cronjobs in WP by loading Scripts via URLs, including Scripts, running Functions, and/or running PHP code. This plugin utilizes the wp_cron API.
All you do is install the plugin, schedule your Scripts / Functions / PHP code to run at a specific interval, and live your life — Cron it up!
<h3>Features</h3>
<h4>Administration</h4>
<ul>
<li>Create and Manage Custom Cronjobs</li>
<li>View Custom Cronjob Activity Log</li>
<li>View and Remove Existing Cronjobs</li>
<li>View Available Cronjob Schedules and Intervals</li>
<li>Reset Logs or all Crony settings</li>
<li>Admin.Class.php – A class for plugins to manage data using the WordPress UI appearance</li>
</ul>

Crony Cronjob Manager

Create and Manage Cronjobs in WP by loading Scripts via URLs, including Scripts, running Functions, and/or running PHP code.

Delete Spam Daily vs Crony Cronjob Manager