ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
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.
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
MTcaptcha - Enterprise Captcha solutions
F5 NGINX - F5 NGINX is a web application security solution that allows you to protect your applications, APIs, and customer data across cloud servers, on-premises data centers, and architectures.
GeeTest CAPTCHA - GeeTest protects your websites, mobile Apps and APIs from bot threats.