Offline access to Gmail, Calendar and Docs has recently been made available to Google Apps domains
Gmail: Gmail Offline is a Chrome Web Store app based on the Gmail web app for tablets.
Calendar: When offline, you can view events and RSVP to appointments.
Docs: You can view documents and spreadsheets offline.
Google Apps, Google Apps for Business, Government and Education
How to access what’s new:
Gmail: Install the Gmail offline app from the Chrome Web store. Administrators need to first allow access to the ‘Chrome Web Store’ service.
Calendar and Docs: Click the gear icon at the top right corner of the web app and select the option for offline access.