We use the email and the calendar. We have a separate account for our calendar and share the password among our shop coordinators. At our monthly meeting we go around and sign up shifts by creating events with our name. Before the sign-up it looks like our regular open shop calendar, then folks create events on the same day as open shops, only with their name.  So a given day will say Open Shop 6-9pm, Justin M, Reda A. Its a free way to organize our coordinator calendar online. We don't really use the documents app much.
Justin Morse
Third Hand Bicycle Co-op