TODO gotta research those more:
Major downsides that most of those personal knowledge databases have:
  • very little/no focus on public publishing, which is the primary focus of OurBigBook.com
  • either limited or no multiuser features, e.g. edit protection and cross user topics
  • graph based instead of tree based. For books we need a single clear ordering of a tree. Graph should come as a secondary thing through tags.