Some outliners are used for to-do lists, calendar editing, or project management. They need to incorporate the notion of events and dates. Sometimes, this includes event dependencies: event A or B must occur before event C does, for instance. Occasionally, an awareness of events is deeply integrated into the fabric of the outliners with alarms, priorities, event displays, and such.

Far and away, the master of this crowd is Schedule. It is an outliner with columns, and some of those columns can represent time periods and be linked according to event dependency rules—like Gantt charts. The screenshot doesn’t do justice to the bewildering array of modeling and presentation options.