I use Rainlendar, a desktop calender which is very comfortable for me and im using it for a long time.

Now i want to synchronize my zimbra calendars with rainlendar.

The problem is that rainlendar do not support CalDav.
It supports only NetworkSharedCalendars through http, https, and ftp.

I know its possible to share zimbracalendars, but synchronizing is only possible in one way because im only able to share public calendars read only.

I also know that its possible to link an external calendar but im not able to link to an external LOCAL calendar. So i would be able to sync through ftp.

Have someone any suggestions to get sync?