Export iCalendar format for pages with an RSS feed
Updated link for above Google help page: Add by URL feature.
If you have any issues, create a new ticket.
Download the zipped source from here.
Click on the Timeline navigation item in a Trac instance where this plugin is enabled. Scroll to the bottom of the page. The ability to download as iCalendar should be apparent:
See the bottom of http://trac.openplans.org/openplans/timeline.
Originally developed at The Open Planning Project.