ModSecurity - ModSecurity is an Open Source web application firewall developed by Trustwave's SpiderLabs.
Barracuda Web Application Firewall - Barracuda Web Application Firewall offers security and DDoS protection against automated & targeted attacks.
Shadow Daemon - Shadow Daemon is a collection of tools to detect, record and prevent attacks on web applications.
AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
ironbee - Universal web application firewall engine
SiteLock - SiteLock software provides advanced website security, daily security scans, web app firewall with a CDN to deliver content more securely.