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.
Imperva SecureSphere - Get the flexibility, reliability, and performance you need to protect your business. SecureSphere covers you both on-premises or in the cloud.
MTcaptcha - Enterprise Captcha solutions
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
GeeTest CAPTCHA - GeeTest protects your websites, mobile Apps and APIs from bot threats.
ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.