DownNotifier.com - DownNotifier knows about website availability and provides notification.
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.
UptimeRobot - Free Website Uptime Monitoring
NetCrunch Tools - Our free network tools offer ping scanning, SNMP scanning, port and network service scanning, and more.
Is It Down Right Now? - Network & Admin
NetTK - NetTK, Network Tool Kit, is an Open Source alternative for monitoring and troubleshooting your...