Google has announced a new Google Labs for Google Apps, much like the labs they have for email. The most interesting part about this is that the infrastructure for this is built on top of the Google App Engine.
There are currently three apps available at their new Solutions Marketplace. These apps can be added to anyone who has google apps for domains.
What's even more interesting is that they allude to opening this up in the future so that developers will be able to offer their appengine apps in the marketplace. If this does happen, it will open up a new market for apps to be sold to companies to used privately on their own domains.