Your main page is focused on content creation, but I think you're missing a key aspect of these kinds of tools -- content searching. Right now, it reads as: thoughts are messy, and your tool enables to think in that messy fashion.... and everything stays messy. My immediate concern is that I can trivially add data to the system, but I can't get it back out (both automatically, by export features, and manually, by navigating it)
Particularly, looking at https://launch-preview.museapp.com/handbook, the inbox/card mechanic seems worth pointing out, and boards/cards as your primary model of higher-level organization.
Also a question: the handbook says boards contain cards, and cards contain boards -- they can be organized as mutually recursive? That's cool. In fact, there are very few of these modern systems that properly let you recurse