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.
Ossec - OSSEC is an Open Source Host-based Intrusion Detection System.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
Samhain - The Samhain host-based intrusion detection system (HIDS) provides file integrity checking and log...
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
Tripwire - Open Source Tripwire software is a security and data integrity tool useful for monitoring and...