Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.

tcpdump - tcpdump is a common packet analyzer that runs under the command line.

Zabbix - Track, record, alert and visualize performance and availability of IT resources

Ettercap - Ettercap is a suite for man in the middle attacks on LAN.

Abusix - Abusix is a network security company that offers email threat protection and network abuse handling solutions to ISPs, Telcos, and Cloud/Hosting Providers to stop the rapidly growing problem of email-borne threats and other kinds of network abuse.

SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.