It's markdown with Excel's ease of creating buttons (in org-mode's case ascii buttons) to execute arbitrary callbacks, e.g., cross referencing, summarizing, sorting, etc.

It primarily appeals to weekly status jockeys (project managers) whose rudimentary programming skills are just good enough to hack some emacs lisp. As someone who doesn't mind grepping an omnibus "notes.txt" file and thinks "literate programming" is a waste of time, I've never found a use for org-mode.