Continuing the discussion from RemNote, It is a Real Horse Race Now:
I’m not sure I can do it justice, having just gotten back into using it. When starting to study a topic, you create a notebook and add books to the notebook. Books can be PDFs, EPUBs, etc. You can then read the documents on one half of the screen, and drag highlights into the workspace of the notebook. These highlights (cards) can then be linked together, notes and pictures added to them, etc. The cool thing is the cards are linked back to the original PDF/EPUB, so you can jump back and see things in context. And, there is much, much more (outlines, flashcards, etc.).
I’ve linked their intro video below. If you’re interested, it’s well worth taking some time to watch some of the Paperless Student and/or Tutoriots videos (linked below).