calendars are useful tools. even paper ones are great for remembering dates, taking out the trash, and keeping track of family birthdays. some of the first mobile apps were datebooks and calendars. they’re useful to this day for exactly the same things as their antiquated paper ancestors. surprisingly, the technology behind calendars has changed very little over the years. most calendar apps are still just massive datebooks with customization features. still, there are plenty of great ones out there. here are the best calendar apps to keep you organized!