Snort is a well-known open source intrusion detection and prevention. It analyze traffic, creates alerts, and record problematic packets. Rules can be customized based on a specific needs. You can download Snort, below.
Security Onion is a Network Security Monitoring and Intrusion Detection based on Linux. It contains Snort, Suricata, Sguil, Squert, argus, Xplico, tcpreplay, scapy, hping, and many other security tools.You can download Security Onion, here.