reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.
Humans Not Invited - CAPTCHA that filters out humans and only lets programs pass
DataDome - DataDome provides innovative technology and human expertise to block bad bots.
DOOM Captcha - Captchas don't have to be boring
MTcaptcha - Enterprise Captcha solutions
Squat Captcha - The worst captcha ever! Forces you to do 10 squats