I've just revisited OwnCloud suite and found that a decent progress has been made to warrant a viable alternative to Google suite of PIM applications. Here is a quick rundown:
NextCloud applications allow downloading calendars as .ics and contacts as .vcf files, which can be used for ocassional backup. If a server goes down, you always have the backup available on your device where the data was last edited.
The next step might be to run own NextCloud instance on Raspberry Pi or something similar.
- Calendar -> NextCloud Calendar online, Mozilla Thunderbird on PC
- Contacts -> NextCloud Contacts online, Mozilla Thunderbird + CardBook on PC
- Sync adapter for Android = DAVdroid
- Tasks => OpenTasks or aCalendar+
- Notes => NextCloud Notes (link) for Android
NextCloud applications allow downloading calendars as .ics and contacts as .vcf files, which can be used for ocassional backup. If a server goes down, you always have the backup available on your device where the data was last edited.
The next step might be to run own NextCloud instance on Raspberry Pi or something similar.