Google has launched a new online store where third-party developers can sell Web apps to Google Apps users. The Google Apps Marketplace offers Web applications that can be integrated into Google Calendar, Google Docs, Gmail, and other services available in the search company's cloud-based productivity suite.

The new store provides developers access to 25 million untapped Google Apps users, which includes some 2 million businesses. The Web apps can be installed in just a few clicks, and function just like native features. To ensure a seamless experience, the apps only require a single sign-on facilitated by OpenID, rather than dealing with separate credentials for each.

Google is charging developers $100 to add an application and then takes a 20% cut of revenue. More than 50 companies are already selling apps, with software including Appirio's Professional Services Connect, Atlassian's JIRA Studio, Intuit Online Payroll, Manymoon project management, Zoho's suite of productivity and collaboration programs, and many others.