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