Hailstorm
Here's Clay Shirky of OpenP2P talking about Microsoft's Hailstorm. He says "Hailstorm adds some meat to the Microsoft .NET initiative. It is a set of Web services whose data is contained in a set of XML documents, and which is accessed from the various clients (or "HailStorm endpoints") via SOAP (Simple Object Access Protocol). These services are organized around user identity, and will include standard functions such as myAddress (electronic and geographic address for an identity); myProfile, (name, nickname, special dates, picture); myCalendar, myWallet; and so on.".
While Microsoft claims to support other operating systems on the client side as well, it is there to see if they keep their word and do not remove support in the future.