Planning to switch from Microsoft Exchange or want to run Microsoft Outlook on Google Apps instead of Microsoft Exchange on your enterprise, then consider Google Apps Sync for Microsoft Outlook. It will be an effective replacement for Microsoft Exchange on the backend. This app allows you to keep Microsoft Outlook but use Google Apps Gmail as the back-end.
Google Apps Sync for Microsoft Outlook allows you to use Microsoft Outlook with Google Apps Premier or Education Editions. It enables Outlook users to connect to Google Apps for business email, contacts and calendar.
Here is the link to Google Apps Sync for Microsoft Outlook.