As strange as many might think it to be, Microsoft has open source initiatives... They just announced yesterday a new Open Source initiative called "FlexWiki". It concerns software for making Wikis... A quick look at the developers for the project (on source forge) and you see the inventor of Wiki, Ward Cunningham (of the Platform Architecture Guidance team at Microsoft).
This is not the only project by Microsoft at source forge. Some of the earlier releases this year include Windows Installer XML (WiX) ans Windows Template Library (WTL).