At Campfire One, Google launched “Google Apps Marketplace,” which allows you to publish applications that integrate with Google Apps and give you access to more than 2 million businesses and 25 million Google Apps users. “Listing your integrated cloud app on GAM enables it to have seamless OpenID, OAuth and Atom Publishing Protocol-based single sign-on with Google Apps. The purchase is a simple "Add it now" button that streamlines provisioning and data authorization steps for admins, and it gives end users a link to your app in their Google universal navigation bar for one click access and single sign-on. There’re three simple steps for a GAM app: 1) Have or create a cloud application and host it on the platform of your choice 2) Integrate your cloud app with Google Apps using available APIs 3) Create a manifest file describing your application and list it for sale on Marketplace. More than 50 applications from companies like Intuit and Atlassian, more coming from companies like NetSuite and SuccessFactors are available on GAM,” noted Google.
More info: More great apps for Google Apps