How does it work?
The main idea is that you upload your audio files to your cloud storage and then consume those through Diffuse. It provides a malleable and cooperative platform along with a set of building blocks that allow you to shape your own (audio) software.
The default setup is focused on playing that audio from various sources, browsing your collection through multiple diverse user interfaces, making playlists, adding items as favourites, etc. Besides the defaults, you can build and share your own interfaces and features.
It provides this using a web application that lives solely in your browser. If you're looking at this on the official diffuse.sh domain, you can pick the version of said web application. There's also the option to self-host. The code is open source.
Why does this exist?
Diffuse exists because I (@tokono.ma) wanted a way to listen to purchased digital music on multiple devices and add it to playlists that are not tied to a particular platform. Later, I also wanted tools to manipulate, manage and inspect those playlists and other data; along with the ability to shape what your music player looks like.