A last call was made on iCalendar in XML Format (xCal-Basic). The draft can be found at: http://www.ietf.org/internet-drafts/draft-royer-calsch-xcal-03.txt
xCal is a representation of iCalendar objects in XML. xCal is not an alternative or next generation of iCalendar. (Emphasis mine)
Response has varied from one side: Why do we need another format as iCalendar is working? to the other: If you are using XML why not fully use all the XML capabilities and shed some of the past iCalendar issues? Both are good questions.
With respect to the why another format question. We see Service Oriented Architectures (SOA) as the future of business, as do many other companies including the top calendaring companies, IBM (Lotus Notes), Microsoft (Microsoft Exchange and Outlook), Novell (GroupWise), plus many others. SOA is primarily enabled by standard-based protocols, such as, the web services stack of XML, SOAP, UDDI, and WSDL. iCalendar ICS files do not play well within this space. For calendaring and scheduling to be part of the future then iCalendar needs to be represented in XML. xCal is this representation. The iCalendar components, properties, and parameters as defined xCal for use in XML.
With respect to question 2, Why not fully use all the XML capabilities? iCalendar is the current prevailing calendaring standard today and to the most part is interoperable between the major calendar vendors. Therefore, trying to propose a new standard that does not take into account the millions of existing users and majority of software in existence would simply not be acceptable. xCal uses an exact 1 to 1 mapping between iCalendar and the XML objects and does not introduce any semantics not already defined by the iCalendar standards.
xCal format was selected to ease translation back to the iCalendar format using XSLT to ensure compatibility with existing calendar clients.
To further ensure compatibility, IntelliCal, has released, xCal2iCal, to open source. xCal2iCal is an application using XSLT, which transforms XML xml:lang attributes into iCalendar LANGUAGE parameters. xCal2iCal can be found at: http://sourceforge.net/projects/icalendar/