  thumb|right|icalendar components and their properties :not to be confused with the apple ical. icalendar is a computer file format which allows internet users to send meeting requests and tasks to other internet users, via email, or sharing files with an extension of .ics. recipients of the icalendar data file (with supporting software, such as an email client or calendar application) can respond to the sender easily or counter-propose another meeting date/time.icalendar is a standard (rfc 5545) for calendar data exchange. the standard is sometimes referred to as "ical", which was the name of the apple inc. calendar program before os x mountain lion (see ical) that provides one of the implementations of the standard. icalendar is used and supported by a large number of products, including google calendar, apple calendar (formerly ical),from ical ibm lotus notes,from lotus notes 8.5 icalendar support info on ibm.com. yahoo! calendar, evolution (software), em client, lightning extension for mozilla thunderbird and seamonkey, and partially by microsoft outlook and novell groupwise. icalendar is designed to be independent of the transport protocol. for example, certain events can be sent by traditional email or whole calendar files can be shared and edited by using a webdav server, or syncml. simple web servers (using just the http protocol) are often used to distribute icalendar data about an event and to publish busy times of an individual. publishers can embed icalendar data in web pages using hcalendar, a 1:1 microformat representation of icalendar in semantic (x)html. ==history and design== icalendar was created by the internet engineering task force calendaring and scheduling working group (chaired by anik ganguly of open text corporation), and was authored by frank dawson of lotus development corporation and derik stenerson of microsoft corporation. icalendar is heavily based on the earlier vcalendar by the internet mail consortium (imc). icalendar data files are plain text files with the extension .ics or .ifb (for files containing availability information only). rfc 5545 replaced rfc 2445 in 
Calendaring_standards Computer_file_formats Internet_Standards