1. A popular tool for command-line manipulation of ports, especially text-based protocols. Often used as a replacement for Telnet. Key Point: Variants of netcat are a popular way of redirecting shell prompts and other protocols. In the past, this was always done in the clear. Today, there are variants such as aes-netcat or crytcat.exe that will encrypt the channel. From Hacking-Lexicon

2. TCP/IP swiss army knife A simple Unix utility which reads and writes data across network connections using TCP or UDP protocol. It is designed to be a reliable "back-end" tool that can be used directly or easily driven by other programs and scripts. At the same time it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities. From Debian 3.0r0 APT