Nagios

http://askubuntu.com/questions/145518/how-do-i-install-nagios

https://www.digitalocean.com/community/articles/how-to-install-nagios-on-ubuntu-12-10

http://nagios.sourceforge.net/docs/nagioscore/3/en/addons.html

http://exchange.nagios.org/directory

http://library.nagios.com/library/products/nagiosxi/downloads/main

/usr/lib/nagios/plugins