Prelude is a new innovative hybrid Intrusion Detection system designed 
to be very modular, distributed, rock solid and fast. 

The Prelude Network Intrusion Detection System is a sensor, that may 
be installed on the same machine as the manager or not, which watches 
network traffic and looks for familiar patterns. This is functionally 
equivalent to (Snort (http://www.snort.org).

WWW: http://www.prelude-ids.org/