AppFlowy is a privacy-first, open-source workspace designed for notes, wikis, projects, and more, giving you full control over your data and customizations.
The linked article says quite a bit about the user experience with the app, but I can clarify the limitations, or lack thereof, a bit further in my own post.
For individuals, the hosted cloud service is free for up to 2 members forever. That is 1 collaborative workspace up to 2 members, and 5 GB of storage.
For small work teams, it is $10 per member per month
billed annually. That would also be the cloud hosted service.
There is also a self-hosted AppFlowy Cloud that you can host yourself (it appears to be free, as I see no mention of registration or cost).
Whether you use their hosted cloud or your own self-hosted cloud, there are desktop and mobile apps that will connect to either.