Yes: https://play.google.com/store/apps/details?id=org.dmfs.caldav.lib https://play.google.com/store/apps/details?id=org.dmfs.calda... https://play.google.com

Yes: https://play.google.com/store/apps/details?id=org.dmfs.caldav.lib https://play.google.com/store/apps/details?id=org.dmfs.calda... https://play.google.com/store/apps/details?id=org.dmfs.carddav.Sync https://play.google.com/store/apps/details?id=org.dmfs.cardd... are two of which I'm aware, but they're not free. They worked well when I had my own calendar server, integrating into the "Accounts and sync" section of the settings, thus providing fairly seamless integration with the native calendar app, for example.