OWASP Coraza WAF is a golang modsecurity compatible firewall library
A simple way to block access to the internet per app
TrackerControl Android: monitor and control trackers and ads
AFWall+ (Android Firewall +) - iptables based firewall for Android
Next Generation Open Source Firewall
Web application firewall in C language uses libevent
Powerfull Web Application Firewall for PHP
Jateway is a general purpose TCP/IP connection proxy
Lomalarga is a VPN-like service based on SSH and Linux.