Everyone loves standard protocols, and now Windows Live Messenger has finally moved away from its own proprietary system to use XMPP (the Extensible Messaging and Presence Protocol). This means that it's far easier to create apps that work well with Windows Live, or even integrate it directly into devices. Currently, third-party apps which connect to Live Messenger (like Adium, eBuddy, or Pidgin) use a reverse-engineered library, but this is the first sign of support for unofficial clients from Microsoft. XMPP's also behind a number of other instant messaging services in use today, including Facebook Chat, Google Talk, and Jabber, so the work done to support one platform will be easily transferred to the rest.
The Windows Team Blog says that its new direction is motivated by its principles of choice in both devices and services. However, Microsoft's decision to try and open up the platform could also be motivated by an almost 10 percent drop in active users in the past two years — presumably with the rise of competing services like Facebook Chat.