vdirsyncer (https://vdirsyncer.pimutils.org/en/stable/) can synchronize bi-directionnaly using CardDav and CalDav, with servers. despite it can save all events in one single file per calendar, it is slow. It is very faster and efficient when creating one file per event (UID.ics). Could we support that ? It opens a lot of possibilties.
The orage project is not maintained anymore and has been archived. Closing bugs.