Zabbix - Track, record, alert and visualize performance and availability of IT resources
Ping Meter Gadget - Customizable, graphical, semi-transparent ping (latency) meter.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
NetTK - NetTK, Network Tool Kit, is an Open Source alternative for monitoring and troubleshooting your...
Prometheus - An open-source systems monitoring and alerting toolkit.
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.