This would be crazy useful -- if I used iOS. ;) Why not a webapp (aside from the obvious reasons). A responsive UI that does the same with a nice jQuery twist would be workable on most webkit browsers and would work on Android, iOS, and the new Blackberry 10.
Yeah. By "OS" i mean "open-source" not "iOS". I was thinking it'd be a web app where you can manage multiple lists each one with categories and items. When you are ready to release you just select the repo and milestone from Github and it creates issues for each of the checkbox items.