Radicale - The Radicale Project is a complete CalDAV (calendar) and CardDAV (contact) server solution.
Baïkal - Cal and CardDAV server
SOGo - SOGo is groupware server with a focus on scalability and open standards.
Xandikos - Lightweight CalDAV/CardDAV server on top of Git.
Roundcube - Web-based IMAP email client
AgenDAV - AgenDAV is an Open Source CalDAV Web application.