In an effort to continue to increase Google Apps adoption among businesses, Google recently launched the Google Apps Marketplace. The apps marketplace includes 3rd party apps that integrate with Google Apps. Chris Vander Mey, project manager for the Google Apps Marketplace wrote:
"Once installed to a company's domain, these third-party applications work like native Google applications. With administrator approval, they may interact with calendar, email, document and/or contact data to increase productivity. Administrators can manage the applications from the familiar Google Apps control panel, and employees can open them from within Google Apps.
With OpenID integration, Google Apps users can access the other applications without signing in separately to each. The Google Apps Marketplace eliminates the worry about software updates, keeping track of different passwords and manual syncing and sharing of data, thereby increasing business productivity and lessening frustrations for users and IT administrators alike. That's the power of the cloud."
In my experience with helping migrate people to Google Apps, one of the reasons people still have to use Microsoft products is because they rely on 3rd party apps that interface with the Microsoft software. The Apps Marketplace is certainly part of Google's effort to free people from Microsoft's grasp.