I’ve been working on a note taking app specifically for literature where the idea is that small groups of writers will come across one another’s notes while they’re reading the same work. By responding to another user’s notes the original note taker then has the opportunity to revisit the note and also a book that they may have finished days, weeks, or months ago. It works alright, and I use it extensively, but as you might imagine taking notes on books is a pretty high hurdle for your average user to get over. I’m still hopeful I can find a small market.