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A standard for group calendaring and scheduling from the IETF. It enables calendaring data to be transmitted and automatically entered into the recipient's schedule. In addition a request for a meeting with free and busy times might be sent, and the recipient's software could book the time automatically and send back the response.

Proposed as a standard to replace proprietary specifications such as in Outlook/Exchange, IBM Notes and Groupwise, iCalendar messages are files with an .ical, .ics, .ifb or icalendar extension.

The IETF Calendaring and Scheduling Standards Simplification group, dubbed "calsify," works on interoperability between different scheduling systems.

The Successor to vCalendar
iCalendar superseded the vCalendar standard developed by Versit, then turned over to the Internet Mail Consortium (IMC) and later the IETF. It added more detail to vCalendar events and defined a protocol for transporting it.
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References in periodicals archive ?
Calendar has been built on the technology of Zimbra, which was acquired by Yahoo!, using the iCalendar (iCal) and CalDAV standards.
You can text your friends about that season finale of Lost, or put the premiere date of Ugly Betty on your iCalendar. Oh, and it makes phone calls too.
HTML, hCard (based on the vCard format), and hCalendar (based on the iCalendar format for events)--few standards are more well-known.
It's compatible with existing messaging systems (Out look, Mobile, IMAP,, POP, iCalendar, RSS, etc.), and its consolidation feature means substantial reduction in managed storage.
Ximian Evolution also supports key data exchange and communications standards, such as IMAP, POP, SMTP, LDAP and iCalendar, and features QuickSearch, vFolders, threaded e-mail view, in-line text editing and synchronization with Palm* handhelds.
Users of the mobile data service can now utilise the iCalendar feature to access and manage their calendars from their mobile phone.