Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
socat - socat is a relay for bidirectional data transfer between two independent data channels.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Komodia Relay - Free open source tool to perform TCP based session relay
Better Uptime - We call you when your website goes down
PortMapper - Do you need to map a specific TCP or UDP port on your machine to another port on another machine?