Mollom - Mollom is a freemium web service to get rid of spam, unwanted content and fake users on your...
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.
OOPSpam Anti-Spam API - The better, new standard to stop spam content.
reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.
AuthKong - A reliable captcha service, offers advanced security to protect websites from spam and abuse while ensuring a user-friendly experience for legitimate visitors.
Akismet - Akismet is a spam fighting service that protects millions of WordPress sites from comment and contact form spam.