A new implementation of STUN and TURN. Full IPv6 support. Supports server authentication with the REST APi by the RFC. Implemented with Erlang.
An RPC server written in Python designed for controlling the firewall rules of a captive portal system.
Oskar Andreasson's Ultimate IPtables Tutorial for Linux. Considered one of the best ways to learn how to set up and use IP tables. Comes in multiple formats and several languages, so there should be something for everybody there.
tutorial firewall iptables linux Byzantium
A website that tests to see if arbitrary URLs are accessible from within China (behind Golden Shield/The Great Firewall).
Cutter is a tool for linux-based firewalls that allows connections passing through them to be forcibly aborted by the firewall administrator.