Zeek is a powerful network analysis framework that is much different from the typical IDS you may know.

Real-time network traffic monitor

NetXMS - Open Source network and infrastructure monitoring and management

Capturing, analysing and responding to cyber attacks

sACNView provides a tool for monitoring and sending the Streaming ACN lighting control protocol used in theatres, TV studios and architectural systems.

Sniff plaintext account/password/cookie on router

Nayuki's updated version of NetPerSec.

QT based app for real-time data visualization from serial or network port

WhyTheFuckIsMyNetworkSoSlow is a network performance analysis tool, making it easy to quickly examine a network and see what is wrong, and to evaluate longer term trends.

A terminal based monitoring tool for InfiniBand networks using Detector (https://github.com/hhu-bsinfo/detector)

A small library for reading the performance counters of all InfiniBand devices in a network

Weak Indication Framework: Efficient C++ library for (Encrypted) Network Traffic Analysis

Low Level Network Monitor - Proof of Concept application, which detects hidden TCP network communication produced by rootkit Pitou.

A graphical network speed meter desktop widget for MS Windows

Napatech packet source plugin for Bro

A simple IOT net speed visualizer with ESP8266 and ILI9341 TFT LCD

Toolkit for working with network data

Network Intrusion Detection System

🔍 ShadowSniff is a lightweight C++ packet sniffer and analyzer built for network monitoring 🛠️. It captures live traffic 🎯, logs packets for review 📄, and includes a Python analyzer for inspecting data 📊. Fully CLI-based, it runs on Linux 💻 and provides a simple, effective tool for packet capture and analysis.