With iOS 5 which Apple released last fall, the Reminders app was introduced. It has a few shortcomings but it’s a fantastic and simple app for keeping track of multiple to-do lists. Its real power comes from the Siri integration (“add apples to my grocery list”) and location awareness (“remind me to do my taxes when I get home”).
A largely unknown feature of iCloud reminders is the ability to share your lists with other iCloud users for collaboration. The reason most people don’t know about it is because you can’t share from your iOS device. You’ll need to do it from the iCloud.com website. Just log into your iCloud account from any computer and visit the Calendar section. Next to each reminder list (and each calendar, by the way) is a little grey “broadcast” button. Click this link to manage your sharing options, including whether you’ll be notified by email when someone else makes changes to the list. The broadcast icon will turn green when sharing is turned on.