Commercial OS X Server, also Open source/cross-platform
Implementation of CalDAV Access and Scheduling. Available as part of the OS X Server software. Also open source. Python-based.
Open source/cross-platform
Implementation of CalDAV Access and Scheduling. Java-based. Includes a Web UI.
Open Source
Java-based server that includes support for CalDAV.
Open Source/PHP/PostgreSQL
Implementation of CalDAV Access and Scheduling with web-based administration.
Open Source/Java
DavMail is a POP/IMAP/SMTP/Caldav/LDAP exchange gateway allowing users to use any mail/calendar client with an Exchange server through Outlook Web Access.
Open Source/Perl/CGI
Dingo is a CalDAV compatible server using MySQL, written in Perl as a CGI script.
Free
EGroupware is an enterprise ready groupware server that includes CalDAV support.
Commercial
Implementation of CalDAV Access and Scheduling.
Open source/cross-platform
Apache plugin implementing CalDAV Access.
Commercial
Implementation of CalDAV Access and Scheduling.
Open Source/cross-platform
Implementation of CalDAV Access.
Open Source (alpha)
SabreDAV is a free WebDAV server and includes support for CalDAV.
Open Source
ScalableOGo (SOGo) is a free groupware server and includes support for CalDAV.
Commercial/Open Source
Implementation of CalDAV Access and Scheduling.
Commercial
Implementation of CalDAV Access and Scheduling.
Commercial/Open Source
Implementation of CalDAV Access and Scheduling.