It seems to me Draft's key growth action is getting users to share a draft with a friend. Design the user's first required action to relate to sharing; capture

It seems to me Draft's key growth action is getting users to share a draft with a friend. Design the user's first required action to relate to sharing; capture the author's email after they click Draft/Save, and their friend(s) emails when they want to share. The interface could use a little work to encourage sharing as well. This product is designed to spread itself inherently, so play to that strength!