Spam-Detecting AI - Spam detection in the physical world
hCaptcha - Do you use a captcha to keep out bots? hCaptcha is a drop-in replacement for reCAPTCHA that earns website owners money and helps companies get their data labeled.
CleanTalk - Spam protection plugins for Joomla, WordPress, phpBB3, IP.Board, vBulletin and etc.
StopForumSpam - StopForumSpam - a database of known forum and blog spam, its sources and the email addresses reported
Akismet - Akismet is a spam fighting service that protects millions of WordPress sites from comment and contact form spam.
Antispam Bee - Say Goodbye to comment spam on your WordPress blog or website.