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.
Virusdie - All-in-One cloud-based, simple, powerful and gorgeous website security tools built for everyone.
GeeTest CAPTCHA - GeeTest protects your websites, mobile Apps and APIs from bot threats.
Sucuri - Website Protection, Malware Removal, and Blacklist Prevention
MTcaptcha - Enterprise Captcha solutions
Wordfence - Comprehensive security plugin for WordPress.