There’s one person I know of who is an enthusiastic user of Obsidian. After seeing them fanboy about it for, like, a year, I finally thought I’d take a look at what it is.
It’s a note app. There are some cool affordances it offers, like built-in synchronization between devices, but fundamentally it’s all about recording, reading, and publishing your process mediated via a glowing rectangle that talks to a server somewhere. So, like, Evernote or something. I get the feeling that it could have some overlap or perhaps synergy with DevonThink (which is also a thing that I don’t use, but I know people who do).
It doesn’t solve a problem I have right now, although I can conceive of situations where I might want to use it. It can, for example, turn a big pile of notes into a wiki, which can be published to a server (or local drive?) so, kind of yay? It uses Markdown, which means that linking one note to another note is pretty easy, and because it parses its notes, it can draw a graph of the note blob as a network.
For now, though, my life is better off with a paper book and a pen.