Windows Live Presence API

Windows Live Presence
From their site: The Windows Live Presence API is an HTTP-based API that returns a Windows Live Messenger user's presence using JavaScript Object Notation (JSON) or an image. The Windows Live Presence API can be used in conjunction with the Windows Live Messenger IM Control. A Web site can show a user’s presence using the Windows Live Presence API and let visitors send messages to the user with the Windows Live Messenger IM Control.