OWASP Coraza WAF is a golang modsecurity compatible firewall library
Cross platform web application firewall (WAF) engine for Apache
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Free UTM appliance: firewall, VPN, WAF and antivirus in one ISO.
Web application firewall in C language uses libevent
A simple Web Application Firewall docker image
Powerfull Web Application Firewall for PHP
Passive or learning mode of web application firewalls to evaluate WAF
Free Web Application Firewall