It’s a very nice note-taking and to-do app, with elements of Taskpaper, Obsidian, Drafts, and Agenda. Pricing starts at $5.99/mo. which is more than I’m willing to pay given that I can do a lot of it with those other apps.
However, I’ve played with it extensively. It’s a great app, and might scratch an itch for you.
Earlier discussion:
Yep. $60 / year for a calendar-linked note taking app is not in the cards. He’s a nice guy, though.
Will it be available on Setapp?
Eventually yes, but not at launch time. NotePlan 3 will launch on the AppStore first, then I’ll add it to Setapp.
No problem waiting for whenever “eventually” is.
What a great piece of software. I’ve been playing around with it since it hit the app stores … and it feels like exactly what I’ve been looking for. I shall keep playing because all of these tools have their pros and cons, and have far more value for some people than others, … but I’m very hopeful.
Noteplan 3 is on SetApp now! 
That’s good news. Be aware that to use NotePlan on iOS/iPadOS devices a per-device Setapp fee of $29.88 U.S. is required. So using NotePlan via Setapp on a Mac, iPhone and iPad will cost about the same as an AppStore subscription to the app.
(I confirmed this by installing NotePlan’s Setapp instance on my phone – it required the iOS Setapp subscription.)
If you’re only using SetApp for NotePlan then it’s a bad deal. But I think NotePlan is $60/yr USD so that additional device cost is still less than the full sub price. 
Unless I’m misunderstanding you some how.