LibreNMS : A fully featured network monitoring system that provides a wealth of features and device support.
SonoBus : SonoBus is an easy to use application for streaming high-quality, low-latency peer-to-peer audio between devices over the internet or a local network....
Postman : Save requests and organize your APIs into Collections. Create and send any HTTP request using the awesome Postman request builder. Write your own test...
Wireshark is the world's foremost network protocol analyzer. It lets you see what's happening on your network at a microscopic level. It is the de facto (and often de jure) standard across many industries and educational institutions.