In a new blog post on the Windows Application Developers blog, Microsoft put up a post describing how to activate Windows 8 contracts in your applications.
A quote from the post:
When you start writing Metro style apps you’ll quickly come across contracts, a new and powerful concept in Windows 8. Metro style apps use contracts to declare interactions they support with other apps and with Windows.
You’ve probably already heard about some of them: search, share, etc. Using contracts, apps become better by working with the system or with each other when users install more apps that implement contracts. In this post I’ll walk you through activation, one of the main concepts to think about as you add contracts to your apps.
You can read the full post here.