openCRX

DAVx⁵ has been successfully tested with openCRX.

openCRX is a professional enterprise-class open-source CRM solution.

DAVx⁵ settings

Base URL: see Wizards / Connection Helper / Profiles / Calendar/Card Profile

openCRX CalDAV/CardDAV collections are read-only by default, but are not flagged as read-only.

Enable read/write access for DAVx⁵, or adding/changing entries will fail.