Looks very interesting. Apparently it uses its own file format. This is a little bit of a problem, because it forces you to rely on this software to access your notes, even if an export to Markdown is possible. But often times these exports of large note databases are not tidy, they may be missing features/information that didn't export well.
So i personally would only ever use a note taking app that is based on text files. This of course is harder to manage, but can be done, like VimWiki or Obsidian have shown.
Maybe if it could be extended for text file as basic storage, it could get a broader user base.
Yes! This way who wants to interact with programming.dev just has to make an account on this or any of the federated servers. Nothing prevents them from having a second account on threads to view all of that 'content' as well.