PortMapper - Do you need to map a specific TCP or UDP port on your machine to another port on another machine?
Statsignal - Statsignal is a simple and cost-effective way to monitor your website or server and publish a status page of your system.
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
OnlineOrNot - Uptime monitoring for software teams (even teams of one).
Komodia Relay - Free open source tool to perform TCP based session relay
Site monitoring - Free open-source website monitoring software, easy to set up and use for monitoring web sites.