I imagine there's a huge group of people, like me, who don't keep fastidious hour-to-hour calendars on Google or Outlook or whatever but whose days could benefit from a little more organization.
Diacarta, a visual day planner, offers that type of organization (and offers it beautifully). The main screen of the app is a small clock that can be populated with icons for all manners of activity-sports, sleep, gold, dry cleaning, working out, etc. Just pick what you need to be doing and drag it to the time of day when you need to be doing it. It might not be quite full-featured enough for people who pack their days with activities like Tetris blocks, but for those who have just been managing by trying to remember where they should be, Diacarta's a beautiful way to stay on top of things.
From the app developers: Unlike any other planner, Diacarta lets you create a mental picture of your day. It's easy. Start with the clock, then choose icons to represent the things on your list. For scheduled events, simply drag the icon to the appropriate place on the clock. Tasks that are not tied to a specific time stay on the screen as a reminder. By tapping on the icon, you can add as much detail as you need for future reference. Star your event when it's complete.