Signal Spam provides email and web client tools to allow you to submit spam emails you have received. These spam emails are then analysed, categorised and added to a database of known abuse. ISP's can subscribe to this database for free to help filter out and block spam.
Say Goodbye to comment spam on your WordPress blog or website. Antispam Bee blocks spam comments and trackbacks effectively, without captchas and without sending personal information to third party services. It is free of charge, ad-free and 100% GDPR compliant.
Anti-Spam Features. CleanTalk protects your website from spam bots and spam in Comments, Orders, Widgets, Registrations, Bookings, And any custom web form, Contact Emails, Subscriptions, Checks the existing comments and users for spam.
It allows you to filter and search for spammer comments on your channel and other's channel(s) in many different ways AND delete/report them all at once (see features below).
Mollom is a freemium web service to get rid of spam, unwanted content and fake users on your Drupal, Wordpress and Joomla site or blog.Discontinued
"The Mollom content moderation service is no longer available … as of 2 April 2018."
Anti-spam plugin blocks automatic spam in comments section. No captcha. Plugin is easy to use: just install it and it just works. Blocked comments can be stored in the Spam area if needed. This can be enabled/disabled via Settings page.