Ettercap NG 0.7

Ettercap NG is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks.

It supports active and passive dissection of many protocols (even ciphered ones) and includes many features for network and host analysis. It works in many platforms but you need a user interface in order to run the program and install some libraries. Some of the user interfaces you can use are the Ncurses based GUI, or the nice GTK2 interface.