Kronolith is the Horde calendar application. It provides web-based calendars
backed by a SQL database or a Kolab server. Supported features include Ajax
and mobile interfaces, shared calendars, remote calendars, invitation
management (iCalendar/iTip), free/busy management, resource management,
alarms, recurring events, and a sophisticated day/week view which handles
arbitrary numbers of overlapping events.

WWW: http://www.horde.org/apps/kronolith/