jsDatePick is a free Javascript date picker, optimized for speed, flexibility, and aesthetics. It can easily be used by webmasters with little to no Javascript experience, or experienced Javascript programmers. We built jsDatePick for our personal finance software, as we were not happy with the available date picking solutions – there is room for a quality date picker that is not tied to any existing Javascript framework, and jsDatePick is it
A calendar plugin that uses Javascript to switch between months in place i.e. without loading or changing the current page. This makes it significantly easier
to install and use than the original plugin, at the cost of likely incompatibility with older browsers in no doubt horrific ways.
Calendar is a Javascript class that adds accessible and unobtrusive date-pickers to your form elements. This class is a compilation of many date-pickers I have implemented over the years and has been completely re-written for Mootools. I have tried to include all the features that have been most useful while streamlining the class itself to keep it as small as possible. 
Continue reading about Calendar A Javascript class for Mootools
The Popup Javascript Calendar pops up a small calendar like VB6 dtPicker and set a text-box value to the user selection. It also highlights the current day, and has a today link.
CodeThatCalendar enables you to easily add the date or time picker to your form or page. Both popup and inline calendars are supported. Features include support for current date and week highlighting, localization, CSS support; Ability to setup start year, date, Configurable scrolling feature, Support for various date formats, Ability to configure the Calendar through the CSS styles, Inline calendar support; Unlimited number of the calendar controls on the same form the page. All titles can be configured so localization of the calendar is easy.
This flexible, simple pop-up calendar is written to work across browsers. It Is fully commented and customisable for language, colours and date format. The pop-up displays a month at a time from a specified range of years. The optional input date determines the initial month displayed.
This JavaScript DatePickerControl allows you to transform your input text control into a date-picker control.
Transform your input text control into a date-picker control. JavaScript Calendar Date Picker control makes it easy to fill out the date/time fields for the website users by selecting the date and time from a popup calendar. 
The Rich Calendar is a cross browser JavaScript calendar script implementing the appropriate functionality with many advanced options widely extending fields of its applications.
There are a lot of JavaScript Calendars out there, but actually only a few can be very customizable to fit anyones need. That is why we have created a Calendar Component that is very customizable and extendable. 