BundleHunt has a number of apps and subscriptions on sale again for a limited time.

https://bundlehunt.com/bundle/2024-superstar-software-bundle/

Cloud Outliner Pro (app is free in the Mac App Store, in-app purchase upgrade to Pro is $9.99) is $1.50 plus $1.43 service fee, paid via Stripe. It's a Lifetime License and includes all future updates.

https://xwavesoft.com/cloud-outliner-for-iphone-ipad-mac-os-x.html

The syncable iOS app is free with a $4.99 unlock:

https://apps.apple.com/us/app/cloud-outliner-nested-lists/id1018143540?ls=1

Don't count on any new features if you do buy iy. I've had the app(s), used lightly, for almost a decade, and I can't remember any feature additions. I primarily use the iOS app to read-only OPML files containing notes and info when I go to convention shows. The Mac app is solid (but basic).

If you use a Mac this sale has some nice pricing on apps like HookMark ($11.99 Standard, $24.99 Pro, around 60% off), and Coherence X, which turns any URL into a Chromium browser 'app' ($3.50, down from $29.99)

This BundleHunt sale is ongoing, but Xwavesoft has also just temporarily reduced the price of the Pro unlocks for all its Mac/iOS apps (in the Apple app stores) by 40%, as part of a Summer Sale.

https://xwavesoft.com/summer-sale-2024.html

Through the iOS App Store the Pro unlock for the iOS app is now $2.99

https://apps.apple.com/us/app/cloud-outliner-nested-lists/id1018143540

and $5.99 for the Mac app (though it remains a bit cheaper through BundleHunt)

https://apps.apple.com/us/app/cloud-outliner-outline-maker/id1024917449