Just got to know about Oxite - an open source blogging platform from Microsoft. Yes! We thought we would never see the day but Microsoft does give away software for free.
Check out the numerous open sources projects on Codeplex - their Open Source community site. Oxite is in Alpha, meaning that it is still in the Internal Test stage. Hopefully they shall have a Beta version out soon ready for public testing. Not sure how it's going to compare to Wordpress but it would definitely need to have more features if they are going to compete against the World's most favourite blog platform. From what I read, they might position it as a full fledged Content Management Systems like Joomla rather than just a blogging platform.