"Link to App Store" widget for mobile web site

For the past months I have found several web sites using some kind of "widget".

If I open a web site having this widget with my iPhone, it will display a link to the (website related) iPhone app. It looks like a simple div containing appname, rating and link. The widget even "knows" whether I have already installed the app or not.

This thing is always shown on the top of the page and looks always the same. Is there some kind of widget/API offered by Apple or who is the creator of those links? I have found nothing yet in the web about it...

You're looking for "Smart App Banners".

http://developer.apple.com/library/ios/#documentation/AppleApplications/Reference/SafariWebContent/PromotingAppswithAppBanners/PromotingAppswithAppBanners.html

Usage is as simple as adding the following meta tag to your web page's source code, specifying the Apple App Store ID some affiliate data, and even a URL scheme argument.

<meta name="apple-itunes-app" content="app-id=myAppStoreID, affiliate-data=myAffiliateData, app-argument=myURL">