I tried Calendar Sync and it was going to by my answer to avoiding Google. However, it has some serious limitations.
As long as you identify each calendar distinctly by using its SOGo Caldav URL, it is able to successfully sync events back and forth and generally works nicely. However, if you have recurring events of any sort in your calendar, it gets completely messed up. The recurring events Vcalendar data is not parsed properly and show up in weird ways in the calendar. This is called out as a limitation on the hypermatix page and was the single biggest reason that I was unable to avoid Google. After trying all possible other options, I have finally succumbed to using Google Calendar with my Android Phone. I'm still looking for alternatives, but have not found one yet. --FiredUp. -- users@sogo.nu https://inverse.ca/sogo/lists