In addition to macOS Sierra, Apple on Tuesday also released updates for its Mac iWork apps to support real-time collaboration. The feature was announced at the iPhone 7 event earlier this month, and was added to iOS apps last week.
Real-time collaboration is exactly what it sounds like. With it, users can work simultaneously in any iWork app regardless of device. A list is displayed of all current document editors, and users see the others' cursor activity in real time.