Designed for organizations in which some users use Google Calendar and other users manage their calendars in Microsoft® Exchange, Calendar Interop enables you to sync thefree/busy status of users in both calendar systems.

This enables users in one calendar system to view the availability of users in the other system before scheduling a meeting.

Editions included:
Google Apps for Business

Languages included:
All supported languages

For more information:
http://support.google.com/a/bin/answer.py?hl=en&answer=1330365