What is iCalendar?
iCalendar is a standard for calendar data exchange. iCalendar allows users to either receive meeting information through email attachments or download it through their web browser.

What do I need to use iCalendar?
You need to use a program or web-based service that can recognize iCalendar files. Wikipedia lists several of the most popular programs and web-based services for reading iCalendar files. Many of these are free of charge. You may also search using the term "iCalendar" on either Yahoo, Google or your favorite search engine