While created by T-Mobile for their devices, the Cozi Family Organizer Shared Calendar and Lists app for the iPad and iPhone can be used by any iOS user. While it does require registration of a new account, both for yourself and for your family, the process is quick and the number of free tools you receive is quite impressive.
Cozi Family Organizer is designed to put all of your family's events, activities, and needs in one interface. Ideally that interface would be organized by each family member, not just one person--though the owner of the account can make changes to everyone's calendars and to-do lists, as needed. The home menu provides four options--calendar, to-do lists, shopping lists, and journal--and you can even customize the home screen with a family photo. Each of the tools is well constructed to display all items from the family, or users can even hone in on a single family member with the tap of a button. While it syncs remotely with other family members, the calendar and to-do list tools don't sync with the existing iCloud items on your device, which means entering a lot of things twice.
Cozi Family Organizer is a well-made app with many strong features. While the ads are occasionally obtrusive and the lack of syncing between the app and iOS data from your calendar or reminder list is frustrating, the setup and execution of a shared family interface is a wonderful tool that a lot of families will find useful.