[Lizard]

Yes and not yet.

Yes, multiple people could access one file (just set the sync settings the same on each person's computer) and make all the same edits a single user could. And you could set up a perspective for completed items, possibly sorted by completion date.

However, this does open up a risk of data loss. If 2 people edit the same item at about the same time, one person's changes could get lost. For example, I change the due date of the action, then you add a note, then we both sync. Your note will get saved and my due date will be lost.

So, really, the answer is "not yet". We want to add some collaboration features to OmniFocus, but have not yet done so.