In response to community pressure, Microsoft has removed project Sandcastle from their CodePlex website. This is a temporary move while they contemplate Sandcastles future.
Sandcastle is Microsoft's answer to JavaDoc. Though in active use at Microsoft for several years, it is still a very rough project and appears to be no where near ready for general deployment. Prior to the release of .NET 2.0 and the announcement of Sandcastle the standard tool was the much more mature NDoc. Unfortunately NDoc is no longer being maintained.
The most recent dispute over Sandcastle is its non-open status. Officially all projects on CodePlex are supposed to adhere to an open source license, preferably approved by the OSI. In reality it has become a dumping ground for stuff that would have been placed in the now defunct GotDotNet site.
Due to popular outcry against having a non-open source project on the site, Microsoft has pulled Sandcastle from CodePlex. According to Anand, Microsoft is considering either moving the project to MSDN Code gallery or republishing the project with the source code. In the mean time you can download the May CTP from Paulo Santos' mirror.