pyHIDS is a simple host-based intrusion detection system.
It uses an RSA signature to check the integrity of its database.
Alerts are written in the logs of the system and can be sent via email to a list of users.
You can define rules to specify files to be checked periodically.
Guardog is a simple but powerful intrusion dectection system (IDS) that works by inspecting messages from log files, network packets, and other sources. It uses Perl regular expressions to check for any bad messages.