When comparing Rainlendar vs Calendar, the Slant community recommends Calendar for most people. In the question“What are the best calendar apps for UNIX-like systems?” Calendar is ranked 1st while Rainlendar is ranked 10th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Integration
Your calendar data doesn't need to be stored with your computer. Data can be retrieved from Google, RTM, and even Outlook. (With the pro version removing annoying unregistered marks)
Pro Blends in with the desktop
This calendar stays out of your way, while remaining readily available to tell you what's coming up.
The Shadow skin make it look like a wallpaper calendar, but has the benefit of being interactive.
Pro Customizable
Take control of your calendar by scripting new functionality, take skins already created, or just disable all the fluff.
Rainlendar provides a platform to present your data in the way you desire.
Pro GNOME native integration
Pro Currently in active development
GNOME Calendar is improved with every release cycle of GNOME.
Pro Simplicity
Calendar for GNOME aims to find the perfect balance between features and usability.
Pro Synchronisation
It has online accounts integration.
Cons
Con Can be unstable
The calendar crashes from time to time when entering new data.
Con Cannot print
Con Extremely buggy
Con Poor interoperability with online calendars
Does not connect to Fastmail.
Con Far too simple
Con FAR too tied into the GNOME infrastructure
The UI and configuration presume you are running GNOME, and has the ugliness of a GNOME application. Configuration, as is usual for any GNOME application, is pretty much nonesistent.
Con Can't read 'all-day' events with dark theme
Text is white on light blue with dark themes. The workaround: assign all-day events to just one hour.
Con Can't import ics files
Con Continues to pop-up reminders that are turned off and they cannot ever be removed
The GNOME Calendar displays pop-ups from an old Google Calendar that was used. That Google Calendar has long since been removed from GNOME, and even with the notifications turned off on the GNOME Calendar, the pop-ups still happen.
Con Incorrect appointment times when importing .ics calendars
Con No support yet for WebCal
No support yet for WebCal, such as those offered by Facebook events.
A workaround exists. Since this application uses the same background services as Evolution, installing it and adding the WebCal calendars there, also adds them to GNOME Calendar.