Google is recruiting allies in its effort to win customers for Google Apps, its bundle of online office software. The search giant just announced a new service called the Google Apps Marketplace.

As the name suggests, it’s an online store where third-party developers can sell their applications to the 25 million users of Google Apps. The third-party apps are integrated with Google’s, so users can access them just by logging into Google Apps, and the apps can access data within Google Apps.

The benefit to Google is that the company can dramatically expand the capabilities within Apps without having to build every new application itself. Google also collects 20 percent of the revenue earned by third-party apps. Developers, meanwhile, get integration with Google products that are a core part of many users’ jobs and get access to a big audience.

The service was announced tonight at Google’s Campfire One event for developers in Mountain View, Calif. I interviewed a Google executive and an app-maker earlier today, but thanks to the somewhat exasperating rules that Google set up around the interviews, I can’t publish that story until 7pm Pacific. In the meantime, expect more posts with details from Campfire One.