Pasteur is a free, in-browser app for generating trippy videos from your music using the legendary Milkdrop visualizer (you may remember it from Winamp). I built the first version nearly 10 years ago, but it required a server running ffmpeg, which added complexity and I eventually shelved it after the MVP.
Recently I discovered WebCodecs for in-browser video encoding and decided to rebuild. Without the server dependency, I was able to rebuild a better version in just a few evenings.
Source: https://github.com/markneub/pasteur
Example output: https://www.youtube.com/watch?v=UkZ3a8I5iMg