ttmap passively analyzes values of TCP Timestamps in captured IP packets. After collecting enough data, it computes characteristic remote machine parameters. These values let it guess remote operating systems and identify unique machines behind a single IP address. For example, it can analyze remote IP load-balanced clusters.
IPTables-tutorial is a tutorial which explains how to install and set up iptables and netfilters on Linux. It takes you through a usable example file step by step, and helps you understand its basic functionality. The tutorial currently contains 6 different example scripts that may be used freely under GPL licensing terms.