hosted at https://rizz0s.github.io/multi-viz/
The multi-viz is a many-handed audio visual machine! I originally wrote it as a feature for an app in vanilla JS (see repo and blog post), but I converted it to a standalone app to help myself learn the React framework.
It has the power to take in and visualize the frequency of multiple sound inputs concurrently. Admittedly, the use cases for that are... slim. But, my suggested one is the Aphex Twin album Druqks. Apparently, it sounds pretty cool if you listen to both volumes at the same time.
This was both one of my first JS and React projects! The stack is complete with JS, React, and the native Web Audio API. :)