Features of eXCalendar include:

Skinnable Interface support ( ability to apply a skin to any background part )
ISO8601 compatible.
Print and Print Preview support.
simple and dropdown versions
date and time support
multiple months in the client area
single or multiple selection
easily scroll to next/previous month, change year, and select date via a simple click
Date spinner support, for the dropdown version
color, font attributes, tooltips, images, markers, for any date
Multi-lines HTML tooltip support
Ability to specify not-selectable/locked dates
Ability to specify non-working days
easy way to load/save the event date collection
customize data format for drop-down version
flat or 3D appearance
supports multiple languages
auto size or fixed size