Host Status Monitor App is a program that allows you to automatically monitor multiple Internet hosts for downtime. It runs from command line or GUI and can visually indicate host status or email you when a machine goes down. Configuration is performed through two files: a program configuration file (hoststatsmonitor.conf), and a list of hosts to be monitored (hostlist.txt).
Panoptes is a scalable, extensible network and host monitoring tool. It includes a dynamic Web management interface based on the Dojo toolkit. It monitors SNMP, TCP port availability, ICMP, HTTP response and content, and SSL certificates internally. It supports monitoring anything else via shell scripts. It also includes a packet capture tool for discovery of hosts, port, and OS.
MN Viewer (Mobile Network Viewer) is a lightweight framework designed for system administrators who would like to be able to monitor many aspects of their network from their mobile phone. It allows for very simple expansion using simple PHP plugins. It is designed to integrate with other monitoring tools such as Cacti.
netstat-monitor is a commandline tool for monitoring network connections. Its output is similar to the output from the netstat command with the options "netstat --inet -alp". Netstat-monitor can be left running, though, and will report new connections as they are made. Also, filters can be created to limit what's displayed to just what's unexpected or interesting.