Homepages:
https://firehol.org/

Reason:
FireHOL is an iptables firewall generator producing stateful iptables packet filtering firewalls, on Linux hosts and routers with any number of network interfaces, any number of routes, any number of services served, any number of complexity between variations of the services (including positive and negative expressions).

It differs from other already included "iptables frontends" with:
It's GUI-less
The configurations stay readable even for very complex setups.
FireQOS is a program which sets up traffic shaping from an easy-to-understand and flexible configuration file.
abstract away the differences between IPv4 and IPv6. so you can concentrate on the rules you want. You can apply rules for IPv4 or IPv6, or both, as you need.
Can be integrated with https://iplists.firehol.org/ - it can update ipsets directly to your computer's kernel, without restarting your firewall. It also optimizes ipsets to allow your firewall have the best possible performance.

Open Source: Yes

Source:
https://github.com/firehol/firehol/releases/download/v3.1.6/firehol-3.1.6.tar.gz