When Google announced that Google Calendar users could read events, the feature was for their Internet domains. Now the offline calendar feature can be used more broadly, though.
The feature is available by clicking the "Offline Beta" link in the upper right side of the page. Clicking on it walks the user through an installation and initial synchronization process.
As with offline Gmail, the service uses Google's Gears software to store a copy of the calendar data on a person's computer so it can accessed while the network is down. Unlike the Gmail version, new items can't be created or modified while offline.
Offline Gmail is available only in some English-speaking countries; it wasn't immediately clear how widespread offline Gmail Calendar access is.
(Via Google Operating System.)