Logwatch (log monitoring)

http://sourceforge.net/projects/logwatch/

OSSIM (SIEM)

http://communities.alienvault.com/community/

Honeyd (honeypot)

http://www.honeyd.org/

ntop (traffic monitor)

http://www.ntop.org/

Nagios Community

http://www.nagios.org/

The Bro Network Security Monitor

http://www.bro-ids.org/

Security Onion

http://code.google.com/p/security-onion/

Aanval

http://www.aanval.com/