PingPlotter - PingPlotter is a troubleshooting tool that helps IT professionals and neophytes identify, diagnose, and resolve network issues.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
SmokePing - Smokeping is a tool for measuring latency.
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.
WinMTR - Free Network Diagnostic Tool. WinMTR is an equivalent of mtr for Windows.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services