Hey, iPhone users don’t get to have all the fun. Google last night announced a new site, Google Apps Marketplace, that will sell (and in some cases give away) applications that will extend the functionality of Google Apps themselves. Google Apps, in case you’ve never used it, is a suite of Google applications (like email, calendar, docs, etc.) that businesses can integrate and use under their own domain names.

The Google Apps Marketplace is available at http://www.google.com/enterprise/marketplace/home. At the moment there are over 50 companies offering applications on the marketplace, which range from products (calendar tools, workflow, sales and marketing, security, etc.) to services (training, archiving, Google Analytics, etc.)

Application/Service pages have details about the applications as well as information on pricing and contact information for the vendor. Furthermore, the page also shows what application access is required for the product/service to function on your Google Apps installation. Every application I looked at already had several reviews from various users — apparently this has been under development for a long time.

Some of the applications are free — for example, the Aviary Design Suite and the standard edition of SocialWok.

When you add an application to your Google Apps installation, here’s what happens. First, you’ll be prompted for your Google Apps domain name and taken to a login screen if it’s necessary. Next, you’ll be walked through accepting the application’s terms of service, then asked to provide access to the different Google Apps data that the application requires. Finally, you’ll be asked to enable the app. Once that’s done, it’ll show up on your dashboard.

You’ll also get a URL to access the application you’ve just installed. Sometimes that’s a prompt to start a new project, sometimes it takes you to a suite of tools that you can immediately use.

As I was playing with this one thing kept bugging me. A post on the Google Enterprise blog talks about the process of enacting an application on your Google Apps domain and notes “some apps require data access, some don’t…so only grant access to apps you trust.” I went and looked at Google’s site for Apps developers, and specifically at the program policies page. The site does note that getting applications approved does require a $100 fee, and that applications are reviewed by Google before they are visible to the public.

But how much of Google’s approval should I invest in trust? In other words, if Google approves an application, is that cause for me to give full trust? How thorough is Google’s review? If Google does find something later is it going to yank the app off the marketplace and alert us?

I do like how many applications are already available, and the idea of having something like Aviary or SurveyMonkey integrated into Google Apps is exciting. But I’ve still got that question about trust…