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https://sabre.io/baikal/ + Davx5 is what I use. Working without flaws and very reliable.
Caldav is what you are looking for. The other comments mention implementations of them and i can vouch for radicale pretty barebones but does its job
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.