It is seems a product from PrivacyTools.io
PrivacyNotes is a Swiss-based, zero-knowledge productivity app that combines notes, tasks, file storage, password vault, and wellness journaling in a single application. It uses E2EE with XChaCha20-Poly1305 encryption and BIP-39 key derivation, ensuring the service provider cannot access user data.
Anyone try Pro plan?
Not really Open Source
Oh. Thank you for your reply @Kris . This is a key point for consider.
Why not use something recommended in Notebooks - Privacy Guides ?
I like Joplin very much. I use it with git sync.
Thank you for your support. It is a good idea. I just consider for some others. I think I will try Joplin and Standardnotes.
I stumbled on privacyntoes the other day. Played around with the free version and committed to early Pro. USD $48 for lifetime access is not bad, and the seed-phrase aspect is a lot like a cryptocurrency wallet which I like.
Some quick notes:
History of PrivacyTools.io and Privacyguides (from the PG Team)
However, Lifetime Labs LLC (incorporated in California, USA I think) now has a part (majority?) ownership stake in PrivacyTools - this definitely seems to be an inflection point for the historic PrivacyTools
On LifetimeLabs
To be fair, it is still in Beta…the licencing aligns with a FOSS model, I can understand that when commencing a commercial enterprise not everything starts as FOSS. If they deliver on their client-side open-sourcing around they full-launch, I think that will be a good signal.
I will give an update after some time spent using the app in Pro.
By the way, inside the app, there are a bunch of default example items (notes, links, passwords) - and one of them is a URL directly to PrivacyGuides itself 
I think there is potentially some real goodwill from this new team.
Tested Task on their demo site and noticed there was no reminder functionality, which is critical for any task management software.
It seems as though they have plans for it unless I’m misunderstanding something. This is on the page you linked as well.
“We have committed to open-sourcing the client apps once the native apps have all shipped. The sync backend stays closed, so that will not make PrivacyNotes an open-source project in the unqualified sense, and we would rather say so than let the phrase do work it has not earned. Until then: open-source clients are the plan, an open core is the present tense.”