ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
Naxsi - NAXSI means Nginx Anti XSS & SQL Injection.
AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
ironbee - Universal web application firewall engine
Imperva Cloud Application Security - Deploy your applications and data where you want. When you want. Imperva keeps them secure in the cloud, on premises, and in hybrid clouds.