A web based calendar

 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.
 .
 This package is part of Horde, a web application Framework written in PHP with
 modules like IMP (webmail), Turba (contacts), Kronolith (calendar), Nag (task
 list), Gollem (file manager), etc.