Microsoft has released an early version of Oxite, it's Open-source Content Management App geared towards developers who build large blogs or expansive websites.
A simple blog engine written using ASP.NET MVC, and is designed with two main goals:
The framework offers many features common in blogs, including pingbacks, trackbacks, anonymous or authenticated comments with the option to moderate comments, RSS feeds for any page and a Web administration panel.
One of the key objectives appears to be the ability to add or create new pages with ease. While it could become a competitor down the road for blog engines such as MovableType and WordPress, that doesn't appear to be the focus at the moment.
More info available at the Microsoft Oxite website.