Monket Calendar is an Ajax enabled online calendar coded in HTML, CSS, Javascript, and PHP. The interface has been designed to make it as easy as possible to add/change/remove events and thereby reduce the frustration of using the browser for entering and managing data. For example, drag and drop events to change dates, drag the start/end of an event to create multi-day events, create and edit events without refreshing the page, all with an iCal style interface.

Requirements: PHP 4+, Apache with RewriteRules enabled support Firefox, Opera, Safari, and Internet Explorer (IE support is still buggy)
Demo: http://www.monket.net/cal/
License: License Free