I love Fantastical for iOS and the new Fantastical 2 for OS X somewhat ironically manages to gracefully bring the small-screen experience of Fantastical to OS X terms. Calendar and Reminders on OS X are not weak spots compared to others (Contacts, for example), but yet I quickly fell in love with Fantastical in under 60 minutes before buying it in the App Store.
Beautiful Pixels has a good write-up that covers some of finer points of Fantastical especially the language processing that makes creating appointments so much easier:
Fantastical’s biggest feature in its iOS and Mac apps has been its Natural Language Parser (NLP) that lets you create new entries using common language. This has been greatly improved in this release, letting you enter strings like, “Remind me to Pay the Credit Card Bill on the 4th saturday of every month” and Fantastical 2 will know exactly what you want to be scheduled. There’s better support for iCloud reminders as well in this release, as Fantastical 2 lets you view your events and reminders together in a single list.