When comparing California vs Evolution, the Slant community recommends Evolution for most people. In the question“What are the best calendar apps for UNIX-like systems?” Evolution is ranked 3rd while California is ranked 9th. The most important reason people chose Evolution is:
Evolution is one of the few Linux desktop e-mail clients that's supports exchange servers.
Specs
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Pros
Pro Integrates with the desktop in order to provide notifications
California offers desktop notification on most major DEs in Linux, which is great to know when events are happening while not having to have the app open in the foreground.
Pro Events can be added using natural language
The application allows natural language input for events. For example, typing in "Lunch with Stuart Kearney at 2 pm" will set the appointment.
Pro Supports exchange servers
Evolution is one of the few Linux desktop e-mail clients that's supports exchange servers.
Pro Great integration with Gnome environment
Pro Manages contacts, tasks, calendar and memos as well
Pro Excellent GPG support
The integration with GPG is excellent. You can sign, encrypt, decrypt, authenticate and verify GPG signatures and GPG signed/encrypted email messages. All of that is just a setting away.
Pro Good support for Google's services
Pro Clean interface with 2 layout variants
Going to View > Preview has the option of switching between "Classical View" and "Vertical View".
Pro HTML rendering is great
Of the many email clients available on GNU/Linux, Evolution has the best HTML renderer. It renders HTML and the entire email content exactly like it would appear on a full blown web browser. Not many email clients are capable of doing that.
Cons
Con Currently not in active development
Yorba, the group that developed California, is no longer actively developing software.
While Geary (Yorba's mail client) has been adopted by the elementary teams as "Pantheon Mail", both elementary and Gnome have their own calendar projects and it is unlikely that either of them will contribute to California in the future.
That being said, California uses evolution data server for all backend/sync/storage related tasks, which should hopefully make it possible to use it even if 3rd party vendors change their APIs/protocols etc. As long as EDS does not introduce backward incompatible changes or any major California bugs occur (it has been working fine for me so far), the current state of California should remain usable for quite a while.
Con Currently no drag and drop support
There is no way to drag events in the app for easy switching, it all has to be done manually which can be a lot of work to move many things around.
Con Can't choose different settings for each mail account
Settings have to applied to all mail accounts.
Con Limited configuration options
Cannot format date as preferred.
Con RAM heavy
Very heavy on RAM usage.
Con Poor integration in any non-GNOME desktop
It is written with GNOME in mind.
Con No configuration messages
Although base functions like bullets, numbered, or pre-formatted text are possible, you can't select or set the font for your messages. Not even serif or sans serif. Which is a bit spartan TBH.
Con Can be wobbly with EWS
Don't be surprised if you have to reboot it a couple of times during a working day, because error messages are piling up (e.g. connection lost, can't sync, can't store appointment, read only). Then again, is this Evolution, or what it connects to? And since such an occasional reboot is dwarfed by the fact that MS365 seems to make full IMAP/ SMTP access (close to) impossible (nice meeting invite, THX, but when is it?), just reboot and get some work done...
Con Only available on Linux
If you have to switch to another platform for whatever reason, you will need to search for a different email client.