Step-by-step checklist for iOS
There's a ton of different ToDo list apps out there. Personally I have used OmniFocus and ToDoIst.
OmniFocus


(subjectively) the nicest interface
sync between platforms with the free OmniSync Service
"Apple" (iOS and OSX) only; not on Windows or Linux; no web interface
not cheap
ToDoIst:
available for all kinds of platforms, including a web interface
free version to get started; premium version with add. features
"template" feature might help you implement and re-use your checklists
tasks can be shared between / assigned to ToDoIst users