I'm looking for an app that will allow me to share a list with another person's iPhone to make a to-do list or a grocery list. I would like it to allow both people to be able to edit/create lists and update in real time. When someone edits the list, I'd like to be able to get a notification that something has been added. Other than that I don't need any additional features- just notifications and mutual sharing/editing of lists. Is there an app like this?