The Deimos Project is a computer statistics/monitoring tool allowing you to gather information and statistics about your computers, including network information and bandwidth, uptime information, keyboard and mouse usage, and hardware information.
WhoisUP monitors hosts via ICMP and shows the status in a webpage. When a host is down, it can send mail, write a syslog message, open a popup message, or play a sound. It uses Nmap to check hosts continuously.