I started using a Macintosh with MORE(Which is now available for free and still works perfectly) a very long time ago (Yes, some of us are still alive). TAO is right on that track ; not trying to look nice, like OmniOutliner, but incredibly efficient.
It's not just a powerful outliner, it's certainly a great writing tool and I advise everyone not to be put off by the appearance of the app.
If you want to be able to write, reorganize your paragraphs, "fold" and "unfold" them, keep a general view of your work, TAO is for you.