For over a year I've been coauthoring a book with someone who lives in another state, and we've tried various tools to pair-review and edit the document.

Obviously Skype has been a huge help here; it's almost better than pairing in person because everyone has a keyboard and a screen instead of switching places and leaning in and all that.

The screen-sharing software has been more problematic until now. My brother recently turned me on to CrossLoop, which is the simplest and most responsive one we've tried, and allows both users to easily type into the document. Kudos to the CrossLoop creators; this really is a big improvement.