Google made the announcement at its Google Campfire One event tonight. The emphasis Google is putting on the enterprise is apparent in how much attention the company put into the event. Over and over we heard that Google passed the 25 million customer mark over the weekend.

It is that mark that Google is using as its hook for attracting developers to its platform. Developers will be charged $100 to join the program. With that entrance fee, they may add as many apps as they wish to the Google Apps Marketplace.

The marketplace supports OpenID to provide a single sign-on for developers. Authorization is integrated into the platform. The customers get access through OAuth, the open standard for authorizing users.

A "manifest page" is the foundation for the service. The developers provides information when adding the application to the marketplace that identifies it. Developers then provide additional information about the product.

The system is a controlled. Application developers submit the app for approval, which might take a few days.

Intuit provided an example of how the system works by showing how payroll could be managed. The customer accesses the account. With Google Apps integration, the customer accesses an account where they have the employee information. It's that collected contact network that is then integrated with the payroll application.

Atlassian showed how Studio, its project management application, would integrate with GMail and Google Apps. Again, if the company is standardized on Google Apps, the information is available through the network.

Manymoon is another project mangement application that was demonstrated. It uses Google Apps to develop features such as a calendar, showing how a startup can leverage Google Apps to add features to its service.

Other companies that were a part of the initial launch include Socialwok and Appirio.

At its core, the marketplace is built upon Google's search capabilities. Google Apps can be extended with applications. In turn, developers have access to the built-in capabilities of Google Apps.

Perhaps the greatest value to customers will be if they are centralized on Google Apps. If so, they can get some pretty powerful capabilities of the marketplace.