When comparing KOrganizer vs Lightning Calendar, the Slant community recommends KOrganizer for most people. In the question“What are the best calendar apps for UNIX-like systems?” KOrganizer is ranked 5th while Lightning Calendar is ranked 8th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Multi-category
Pro Long-time support
Pro Integrated into KDE
It can be used by clicking on the datetime in the bottom right corner.
Pro Imports well from Google Calendar
Pro Easy and intuitive to use
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 Search events by text shows empty results for existing events
Con Has issues with recurring events with exceptions
Has trouble with recurring events that have exceptions to them. If recurring even has an exception to the pattern at some point KOrganizer seems to not display any of the recurring events. Thus making it useless for complex calendars. After verifying that the akonadi back end did have the full set of events, KOrganizer just does not interpret them correctly.
Con Does not connect to secure CalDAV server
Con Does not connect to Fastmail
Con Crashes even whilst trying to launch the app
Con Crashes when trying to add new event
Con Requires KDE
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".