A group of people I really like in Microsoft (they are a fun team) released their very interesting work as a preview. This type of work is very relevant to cross-organization collaboration, virtual organizations, Grids, etc.
“The Security Policy Assertion Language (SecPAL) provides a flexible and robust declarative authorization language developed for large-scale Grid Computing Environments. This installable MSI includes a preview release of the .NET implementation of SecPAL, developer document describing the SecPAL programming model and scenario based samples intended to support evaluation of SecPAL.”