Zabbix - Track, record, alert and visualize performance and availability of IT resources
Multiping - Get MultiPing Support. Network monitoring in 60 seconds. MultiPing provides a graphical view of network performance, monitors hundreds of targets, and sends automatic alerts..
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.
SmokePing - Smokeping is a tool for measuring latency.
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.