pynetfilter_conntrack is a Python binding for libnetfilter_conntrack that allows you to manipulate Netfilter's stateful inspection objects. This makes it possible to easily close connections and obtain information about connections such as the number of packets and bytes. It could be used to create conntrack entries, replacing heavy kernel modules for complex protocols such as FTP and H323.
SOFI is a complete firewall solution for OpenBSD. It is designed for use as an Internet gateway to share an Internet connection among several computers. It provides network address translation (a.k.a. IP masquerading), packet filtering, port forwarding, DNS service, DHCP service, VPN service, and traffic statistics.
Lokiwall is a firewall script for Linux. In addition to the standard function of easily limiting network traffic, it features dual routing (using two Internet connections simultaniously), connection fail-over, load balancing, traffic control, advanced masquerading, advanced DNAT, and advanced marking (to direct specific traffic to a certain interface). The advanced features require some kernel patches. The standard features will work on a default Linux system with iptables and iproute2.