ACal Project
   A PHP calendar project that does not require a database server and is easy to install, setup, and use. [Open source, GPL]
   http://acalproj.sourceforge.net/

Active Calendar
   PHP class that generates calendars (month or year view) as HTML tables (XHTML-Valid). The layout can be configured using CSS, and JavaScript is not required. [Open source, LGPL]
   http://freshmeat.net/projects/activecalendar/

Easily Simple Calendar
   Simple PHP calendar script that is easy to customize.
   http://www.easilysimplecalendar.com/

HIOX Monthly Calendar
   A PHP/Javascript script to show monthly calendar. [Freeware]
   http://www.hscripts.com/scripts/php/calendar.php

Keith Devens PHP Calendar
   A simple, but complete, PHP script to print out a calendar.
   http://keithdevens.com/software/php_calendar

MicroCal
   A calendar solution for dating or membership website. It allows running as popup, or being built in page or even in a form in script. [Free with crypted source code and commercial versions]
   http://calendarscripts.info/index.php?action=product&id=1

MyCalendar
   PHP4/MySQL calendar featuring recurring entries, holiday calculations, optional categories, language packs, numerous search and display options.
   http://abledesign.com/programs/MyCalendar/

PHP Availability Calendar
   A PHP calendar script that shows availability of your rental based on calendar data. [Commercial]
   http://www.merenkov.com/calendar/

PHP Calendar by Cascade
   A customisable PHP 3/4 calendar class.
   http://www.cascade.org.uk/software/php/calendar/index.php

Project Based Calendaring System (PBCS)
   An open source web-based system designed to be a useful tool for project managers or planners.
   http://www.pbcs.org/index.php

Proverbs Web Calendar
   Shows a month format with a popup window detailing the events of each day as they are clicked on. The title and colors are fully customizable within a single file.
   http://www.proverbs.biz/opensource/calendar.php

SCA-Calendar
   A PHP5/MySQL or SQLite calendar based on the SCA class library. It supports recurring entries, categories, dynamic holiday calculation and has a sophisticated rights management. [Open source, GPL]
   http://www.project-sca.org/subprojects/sca-calendar-en.html

Schedule Organizer
   Allows a customer to schedule an appointment via a company's homepage.
   http://www.schedule-organizer.de/en/

WebCalendar
   A PHP application used to maintain a calendar for one or more persons and for a variety of purposes. In addition, the calendaring system is well documented. [Open Source, GPL]
   http://www.k5n.us/webcalendar.php