Chris Buck

This plugin deletes duplicate posts from the database, without affecting menus, each time a new post is published. This is an improvement over other similar plugins that would constantly delete custom menus. This plugin works automatically in the background once it is enabled.
The plugin will automatically delete posts with the exact same post title as a previous post, leaving the original post undisturbed. This is particularly useful for when you have syndicated content or auto-posts that result in erroneous duplicates. The original will remain, and all the duplicates will be deleted, allowing you to preserve your page views on the original.

Super Post Cleaner

Deletes duplicate posts from the database (without affecting menus) each time a new post is published.

prondzyn

The plugin is adding a new WP-Cron event which automatically removes all spam comments older than 7 days.
For the proper functioning requires a properly working WP-Cron. If the plugin does not work please check you have WP-Cron correctly working.

Automatic SPAM Eraser

The plugin is adding a new WP-Cron event which automatically removes all spam comments older than 7 days.

Super Post Cleaner vs Automatic SPAM Eraser