Like Inbox and Messenger, Google's own Calendar app is a brilliant example of Material Design in action. Bright colors, pleasing images, and fast and informative animations all combine to make a great calendar app experience. Google Calendar's full-month view is pretty basic, but agenda list and homescreen widget are wonderfully done. Nexus device users likely have Google Calendar already on their phones, but the rest of us can download it for free from the Play Store now.