Firestarter (firewall)

Firestarter is a personal firewall tool that uses the Netfilter (iptables/ipchains) system built into the Linux kernel. It has the ability to control both inbound and outbound connections. Firestarter provides a graphical interface for configuring firewall rules and settings. It provides real-time monitoring of all network traffic for the system. Firestarter also provides facilities for port forwarding, internet connection sharing and DHCP service.

Firestarter is free and open-source software and uses GUI widgets from GTK+. Note that it uses GTK2 and has not been upgraded to use GTK3 so the last Linux distributions it will run on are Ubuntu 18, Debian 9, etc.