Anyone know of a good checklist/to-do app for iPhone like this?

I’m looking for an iPhone app that can do outline-style checklists with collapsible levels of unlimited depth. It would show how much of a branch of the outline remains to be done, even when it’s collapsed.

The closest thing I’ve found to my ideal is ZeptoLiner, but it doesn’t show how much of a level has been done or remains to be done when it’s collapsed; in fact, the top of a level has its own independent checkbox, which doesn’t necessarily relate to the checkboxes under it.