I also looked at Midnight Inbox (Classic) again. It actually comes really, really close, but its selection of workable tasks from its hierarchy is maddeningly backwards. Basically, you can have lists embedded within lists, but it presents to you as workable the first (uncompleted) item in each list, regardless of its position in the hierarchy. For example, in this list:
  1. Major Task
  2. Major Task
    1. Subtask
      1. Item
      2. Item

it selects 1, 2.a, and 2.a.i as the workable items, while I want them to be 1, 2.a.i, and 2.a.ii.
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Bitt Faulk