I use Org mode in Emacs, mainly because it's plain text and I search through years of notes and documents in seconds using find, grep, ripgrep, etc, also trivial to version control plain text.

If I weren't an Emacs user, I would probably use markdown and any text editor. Actually at work, we do just that for our 5 person team.

Nowadays there are also nice (cross-platform) systems to organise markdown notes, like LogSeq or Obsidian.