[zvr]

The UNIX filesystem has traditionally been a graph for ever. I haven't looked at details for a couple of decades, but definitely all UNIX/POSIX/Linux filesystems operate on a graph model.

A distinction I used to make when I was teaching this stuff: on your filesystem tree, on Unix names (labels) are on the links (arrows), while on DOS/Windows names are on nodes (boxes).

If you want to explore a tag-based system, take a look at https://www.tagspaces.org/