IPFilter
Software
IPFilter is an open-source software package that provides firewall services and network address translation for many Unix-like operating systems. The author and software maintainer is Darren Reed. IPFilter supports both IPv4 and IPv6 protocols,... Wikipedia
License: Before 4.1.35 and 5.1.1: IPFilter License (BSD-like); Since 4.1.35 and 5.1.1: GNU GPLv2