You can download the latest build of the Mozilla calendar extension or of the Sunbird standalone application from www.mozilla.org/projects/calendar/download.html [1].
The Usenet newsgroup netscape.public.mozilla.calendar is where many calendar-related discussions and announcements take place.
Some good information about iCalendar files can be found at developer.apple.com/internet/appleapplications/icalendarfiles.html [2]. A more general overview of the iCalendar project is located at developer.apple.com/internet/appleapplications/icalendarfiles.html [3], although it appears to be somewhat out of date.
Google Maps: maps.google.com [4]
Links:
[1] http://www.mozilla.org/projects/calendar/download.html
[2] http://developer.apple.com/internet/appleapplications/icalendarfiles.html
[3] http://developer.apple.com/internet/appleapplications/icalendarfiles.html
[4] http://maps.google.com