Ixchariot - Instant performance assessment of complex networks from pre- to post-deployment.
Uptime Kuma - A fancy self-hosted monitoring tool.
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
Statsignal - Statsignal is a simple and cost-effective way to monitor your website or server and publish a status page of your system.
PsPing - PsPing is a command-line utility for measuring network performance.
UptimeRobot - Free Website Uptime Monitoring