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.

reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.

mosparo - the modern spam protection

AuthKong - A reliable captcha service, offers advanced security to protect websites from spam and abuse while ensuring a user-friendly experience for legitimate visitors.

MTcaptcha - Enterprise Captcha solutions

Mollom - Mollom is a freemium web service to get rid of spam, unwanted content and fake users on your...