When comparing Fantastical 2 vs Rooster calendar, the Slant community recommends Fantastical 2 for most people. In the question“What are the best calendar apps for iPhone?” Fantastical 2 is ranked 1st while Rooster calendar is ranked 21st. The most important reason people chose Fantastical 2 is:
Fantastical makes it really easy to add events using their superb natural language parser. For instance, an entry like "breakfast at 9am at The Diner" will be handled correctly. In addition to their best in class natural language processing, Fantastical has awesome features such as allowing users to append "/work" or "/personal" in order to add events to the specified calendar and setting up abbreviations that will add snippets of text.
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Pros
Pro Very polished natural language text entry
Fantastical makes it really easy to add events using their superb natural language parser. For instance, an entry like "breakfast at 9am at The Diner" will be handled correctly.
In addition to their best in class natural language processing, Fantastical has awesome features such as allowing users to append "/work" or "/personal" in order to add events to the specified calendar and setting up abbreviations that will add snippets of text.
Pro Awesome syncing support
Google, iCloud, Facebook, CalDAV, Exchanged, and iPhone calendar are all supported out of the box.
Pro "Dayticker" is a great way to quickly see appointments
Although pretty simple, the Dayticker view, located at the top of the user interface, is simply fantastic for quickly seeing which days are booked out. It also acts as a convenient way to add new events (long press on a day).
Pro Displays inline map of the event's location
The app displays inline map of the event's provided location. Additionally, users can choose between Apple's Maps or Google's Maps applications to use the feature with.
Pro Allows adding reminders
Using the natural language parser, reminders can be added with the keywords "reminder", "todo", "task", or "remind me to."

Pro Syncs with iOS reminders
Existing reminders can be used or adde with Siri.
Pro Functions as a widget
With Fantastical 2, the calendar can be accessed through a widget in order to save time.
Pro Gesture driven
Fantastical 2 lets users flick, scroll, and swipe to quickly move through different views and types of information.
Pro Custom colors
Tasks can be color coordinated in order to see their categories at a glance.
Pro Resizeable window
The divider between the two views can be dragged for customized viewing.
Pro Combined Calendar and To-Do List
It lays out your tasks and events each day, making it easy to stay on top of things. It has a pin board for tasks that are important, 'someday' or just dont belong to dates.
Pro Beautiful UI
UI is awesome, better than the standard calendar app which is a bit bland, and has far too many layers. Rooster keeps things simple with it's single view design, making it easy to see everything you need to do at once.
Pro Summary View
Rooster gives you the option to just see your 'daily headlines', which is a handy summary of your days. It's great for when you're busy and just want to see what's coming up.
Pro Quick and easy to add appointments
Rooster makes staying organized on mobile easy. It has it's QuickCal keyboard that lets you enter your appointments in just a few taps.
Cons
Con Uses “dots on a day” style interface
This is not the way calendars should work.
Con V2 discontinued, V3 too expensive as a subscription model
Con Only one way to display your events
It would really help to have an actual calendar with the events written into it instead of a list and dots.

Con Have to pay again for the iPad version
Con Not as good as Moleskine cal
