Apple's online cloud service, iCloud, allows you to seamlessly transfer data such as calendars and contacts between iOS devices. You can now access more of this information on iCloud.com. With their updated site. Inline with OS X Mountain Lion desktop apps you can now access web versions of Notes and Reminders.
The UI has had a few updates too, notably in the Find My iPhone app and Calender notifications also appear in the iOS and OS X typical red circle style. To use the new apps on iCloud.com just log in and they will appear, complete with the data from your Mac, iPhone, iPad or iPod Touch if you have iCloud syncing on for Notes and Reminders.
iCloud is a free service from Apple for iOS devices using iOS 5 or later and Mac OS X Lion or later.