My personal knowledge base is hosted on GitHub at
https://raphaelsty.github.io/knowledge/. It scans the documents I like every day using GitHub Action, Zotero, HackerNews upvote and Github Likes. It's not yet optimized for smartphones. It cost me $5 to host it for a year.
Would be even better if AI systems were integrated with hypergraphs of the sort, which was an approach some AGI projects were taking 1-2 decades ago.