DAVx⁵ has been successfully tested with Horde.

Horde is a free and open-source Web-based groupware. It provides a PHP-based framework and applications which are built on top of this framework, as the Horde IMP email client, a groupware package (calendars, notes, tasks), a wiki etc.

DAVx⁵ settings

Base URL: /rpc.php/ (e.g. https://server.example/horde/rpc.php/)

Contact group method: No CardDAV contact group support. Choose "per-contact categories" as contact group method to minimize problems.

Known limitations

Horde Turba modifies uploaded contacts (VCards) and drops unknown fields, like certain telephone number/email address types, information about preferred numbers, etc.