I've experimented with most outlining software, including Opal, but find I've gradually jettisoned them all in favour of Obsidian, which has very acceptable outlining support. And I've just discovered a plugin that supports scrivenings (like Ulysses, Scrivener, etc.), which I may start experimenting with (the developer was laudably open about a rather ghastly bug in an early version, which IMHO is a good sign!). We'll see! (Sorry, for those interested, the plugin in question is called textFlow.)

I suspect Bill has a plugin-endorsement deal with Shida and Erica.

I might be a bit mean, but instead of the 7-day trial period mentioned on the website, the app says ‘6 days remaining’ as soon as you open it for the first time...

If only! And... I've had to uninstall textFlow because it's not working properly in my particular installation. Ah well, win some, lose some! BeautyTasks, on the other hand, is rapidly becoming a favourite... ;-)

Paul Korm wrote:

I suspect Bill has a plugin-endorsement deal with Shida and Erica.

Ah, yes, NeO Outliner. I confused NeO Outliner with Opal. I just checked Neo Outliner's availability, and it is still available in the macOS App Store, with the most recent update being one month ago. A trial version is available at the developer's website (which appears in Japanese on my Mac):
https://d-lit.com/macosx/neo_outliner/index.php

satis wrote:

By 2006 time I'd moved on to other outlining methods, dabbling with Takashi Hamada's TAO and its successor NeO (one of the few outliners offering cloned items a la MORE), but settled in with OmniOutliner (which I rely on to this day). I got Opal to make sure I could still access my oldest Acta outlines. (Unfortunately Dunham jettisoned additional features from Dyno Notepad like audio attachments, which I subsequently lost access to.)