It's an online collaborative simple document editor/space where you can embed live web stuff into these virtual "pages" and hyperlink between them. It came out

It's an online collaborative simple document editor/space where you can embed live web stuff into these virtual "pages" and hyperlink between them. It came out of Dropbox' acquisition of Hackpad (which itself was based on open-source Etherpad). Funnily enough, Google bought Etherpad and then I suspect that's what they used to create the revolutionary Google Wave in 2009, which of course they killed off years later (just to recently launch Smart Canvas or whatever it's called which is reminiscent of Wave). It's a cool product though, and I still (disclaimer: an ex-Dropboxer) use Dropbox Paper for lots of stuff (especially long form writing and research).