Wireshark is an open source network sniffing utility to analyze network traffic.

KisMAC is a wireless network discovery tool for Mac OS X.

Intercepter-NG is a multifunctional network toolkit for various types to recover interesting data from the network stream and perform different kinds of MiTM …

tcpdump uses the libpcap library to capture packets.

Ettercap is a comprehensive suite for man in the middle attacks.