This looks neat. The comparison has been made to Google Docs, and obviously it's similar, but I can't help but feel it's almost identical. What are the differences?
But fundamentally it is a difference of design intent. Hackpad is not a replacement for a word processor. It is not designed for cosmetically designing papers or reports. Hackpad has been designed from the ground up for collaboration on ideas and for living documents (which evolve over time). It's in use in a number of leading tech companies (airbnb, stripe, upworthy) as well as on the open web.