OWASP Coraza WAF is a golang modsecurity compatible firewall library
Free UTM appliance: firewall, VPN, WAF and antivirus in one ISO.
Web application firewall in C language uses libevent
OWASP ModSecurity Core Rule Set (CRS) Project
Bash script to enable the firewall on startup of your Ubuntu server.
Jateway is a general purpose TCP/IP connection proxy
network control and reporting
Lomalarga is a VPN-like service based on SSH and Linux.