Last night Google launched their Apps Marketplace for Google Apps. I think that this is a good move by Google because it gives another reason for companies to consider using Google Apps for their businesses. If you are a Google Apps customer and you need an application that Google doesn't provide you can search through their marketplace and find a third party app that can integrate with your data in Google Apps (contacts, docs, emails ....).
It will be interesting to see how this evolves when the Chrome OS is launched at the end of the year. I bet Google will make a consumer version of their App Store so that anyone with a Gmail account will be able to buy and add web apps to their Google account.
