non ne ho mai avuto bisogno ma per curiosità ho ravanato in synaptic.

copio e incollo:

1)PHP-Based multi-user calendar
WebCalendar is a PHP-based calendar application that can be configured
as a single-user calendar, a multi-user calendar for groups of users,
or as an event calendar viewable by visitors. MySQL, PostgreSQL, Oracle,
DB2, Interbase or ODBC is required.

2)phpGroupWare calendar management module
phpGroupWare is a fully web based groupware system. It includes applications
such as email, calendar, todo list, address book, file manager, notepad.

This phpGroupWare module provides a calendar scheduling module with
alerts for high priority events