StopForumSpam - StopForumSpam - a database of known forum and blog spam, its sources and the email addresses reported
CleanTalk - Spam protection for WordPress, Joomla, Drupal, and any other websites
reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.
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.
Mollom - Mollom is a freemium web service to get rid of spam, unwanted content and fake users on your...
Antispam Bee - Say Goodbye to comment spam on your WordPress blog or website.