Fping (open source) - fping is a program to send ICMP echo probes to network hosts, similar to ping, but much better performing when pinging multiple hosts.
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.
NetTK - NetTK, Network Tool Kit, is an Open Source alternative for monitoring and troubleshooting your...
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
NetCrunch Tools - Our free network tools offer ping scanning, SNMP scanning, port and network service scanning, and more.
Better Uptime - We call you when your website goes down