If you've used Microsoft Project you know that one of the main features is the ability to traverse your list of tasks, milestones, and groups of tasks in an outline format. Have you seen an outliner other than MSP that comes close? Is there an XML vocabulary/model for outlining or project events/tasks?

To my mind the key difference is the notion of multiple dependency. A leaf may depend on one or more other leafs' start dates or end dates as the cue for its own start or end date.

I was thinking of this in a slightly different way. One thing that Microsoft Project doesn't handle this very well, and MacProject only slightly better is subprojects. That is, each task in a project may be decomposed into a collection of subtasks, which are, in-turn, decomposable. This is an hierarchy that, when sorted properly, forms an outline. Multiple dependency is not an issue to this view of a project.

Another notion would be to consolidate tasks together into families of tasks. While all of the tasks would be at the same level from the point of view of the project plan, they would be grouped into collections, which can be viewed as an outline. Again, multiple dependency is not an issue.

Kurt