When comparing BusyCal vs Lightning Calendar, the Slant community recommends BusyCal for most people. In the question“What are the best calendar apps for Mac OS X?” BusyCal is ranked 1st while Lightning Calendar is ranked 12th. The most important reason people chose BusyCal is:
Alarms may displayed in the BusyCal Alarm Window or the Notification Center. Snooze alarms for any duration, including x minutes before start, Set default alarm intervals for new Events, To Dos, All-Day Events, and Birthdays & Anniversaries.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Custom Alarms and Snoozes
Alarms may displayed in the BusyCal Alarm Window or the Notification Center. Snooze alarms for any duration, including x minutes before start, Set default alarm intervals for new Events, To Dos, All-Day Events, and Birthdays & Anniversaries.
Pro Latteral bar
Pro Weather, moon-phases and graphics
Display a live 10-day weather forecast and moon phases. Drag-n-drop images into your calendar with the Graphics palette. Customize event fonts, sizes, styles and colors.
Pro Custom number of days/weeks
You can customize the number of weeks shown per month, or days shown per week
Pro Great support and development team
Pro Smart Filters
Create Smart Filters to display Calendar Sets, a custom view, or events that match a certain criteria with a single click.
Pro Integrated To Dos
To Dos can be displayed directly in your calendar and carry-forward until completed. To Dos in BusyCal are compatible and sync with the Reminders app on OS X and iOS.
Pro Snappy and light on resources.
Pro Sync with OwnCloud and others
Connections are more stable than in Calendar.
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 Expensive
Con No MS Teams Meeting Integration
Con Displays parallel tasks strictly without overlap
This can lead to not being able to read text in Week view.
Con OSX and iOS Only
Keeps you tied into the Apple ecosystem, not that it's a con, just an observation.
Con Doesn't have a widget
Doesn't contain a widget for the Today section in the Mac Notification section.
Con Doesn't support sync of event colors from a Google calendar
Con Online sync only
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".