Suricata (software)

Suricata is an open-source based intrusion detection system (IDS) and intrusion prevention system (IPS). It was developed by the Open Information Security Foundation (OISF). A beta version was released in December 2009, with the first standard release following in July 2010.

Free intrusion detection systems

 * OSSEC HIDS
 * Prelude Hybrid IDS
 * Sagan
 * Snort
 * Zeek NIDS