When comparing Fantastical 2 vs Lightning Calendar, the Slant community recommends Fantastical 2 for most people. In the question“What are the best calendar apps for Mac OS X?” Fantastical 2 is ranked 3rd while Lightning Calendar is ranked 12th. 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 Free, open source
Lightning Calendar (just as Thunderbird) is completely free and open-source meaning that anyone can use it as well as look through the code or even use the code for their own projects.
Pro Easily keep track of tasks
Bundled in with the calendar options is a tasks option that makes for an easy way to keep track of tasks in the same location as ones events.
Pro Cross-platform
Wherever Mozilla Thunderbird can be installed, the Lightning calendar can follow:
Windows
Linux
MacOS
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
Con Available only as part of Thunderbird
No standalone version of the calendar app is available. And if you're just interested in Lightning Calendar and not Thunderbird, the app will have additional functionality and interface elements that will get in the way of using the calendar.
Con Does not always clear old events from the display, even when the event has been deleted
When accessing Google Calendar, every check shows that the event does not exist anymore.
Con No full CalDAV support
CalDAV support is more hackish than working reliably. E.g. certain fields are not supported, or alarms can lead to duplication of events or changes being reset. As CalDAV support is not truly built-in, and the extension does not have a high quality.
Con Requires third-party gmail integration
And it's not supported in 60+. Use the old versions if you want anything to work.
Con Not for all the versions
You have to downgrade Thunderbird just because Lightning didn't upgrade to the last beta version.
Con Long term availability/ support
Although Thunderbird has an impressive track record and many years of reliable service, its continued existence has been doubtful more than once). For now, all seems good, but it would not be surprising if tomorrow it turns out Thunderbird "has left the building".
Con GUI makes you feel like it's 1995, and not in a nostalgic way
