Ethereal - Ethereal is a network protocol analyser, useful for capturing traffic across non-switched networks.
Ettercap - The type of thing that’s used for naughty man in the middle attacks as outlined here →
Nmap - Useful for discovering a certain type of machine / software version on the network. Can be used for exploit scanning on the ‘net.
Metasploit - The basic function of the framework is a module launcher, allowing the user to configure an exploit module and launch it at a target system.