Windows Live Messenger IM Control contains technical information for developers to enable web sites to show the presence of Windows Live Messenger users, and let site visitors engage in instant messaging conversations with the Messenger users.
Windows Live Presence API contains technical information about using the Windows Live Presence API, an HTTP-based API that returns a Windows Live Messenger user's presence using JavaScript Object Notation (JSON) or an image.
The Windows Live Messenger Activity SDK contains technical information about how to develop and test single-user and multiuser applications by using the Activity object model.