netcat - Netcat is a featured networking utility which reads and writes data across network connections...
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.
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
UptimeRobot - Free Website Uptime Monitoring