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.
GeeTest CAPTCHA - GeeTest protects your websites, mobile Apps and APIs from bot threats.
AuthKong - A reliable captcha service, offers advanced security to protect websites from spam and abuse while ensuring a user-friendly experience for legitimate visitors.
DataDome - DataDome provides innovative technology and human expertise to block bad bots.
CleanTalk - Spam protection for WordPress, Joomla, Drupal, and any other websites
Akismet - Akismet is a spam fighting service that protects millions of WordPress sites from comment and contact form spam.