reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.
DOOM Captcha - Captchas don't have to be boring
DataDome - DataDome provides innovative technology and human expertise to block bad bots.
GeeTest CAPTCHA - GeeTest protects your websites, mobile Apps and APIs from bot threats.
MTcaptcha - Enterprise Captcha solutions
Humans Not Invited - CAPTCHA that filters out humans and only lets programs pass