You can invite additional users to your story. Co-workers, freelancers, translators, it's up to you!
Just click on the Invite button located at the upper-right of a story to get started. You will then be presented with a dropdown list of current users to invite. The option to create a new user is also available.
Don't worry - only writers and publishers can see all users. Guest writers will not be able to see other guest writers.