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 7th while Lightning Calendar is ranked 11th.
Ranked in these QuestionsQuestion Ranking
Pro Latteral bar
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 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 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 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 Great support and development team
Pro Free, open source and cross-platform
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.
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 Not to all the versions
I had to downgrade my Thunderbird just because Lightning didn't upgraded to the last beta version....and I can't live without Lightning.