Intellipedia: An interesting article about the wiki used inside the U.S. intelligence community.
Intellipedia consists of three wikis that run on JWICS, SIPRNet, and Intelink-U. They are used by individuals with appropriate clearances from the 16 agencies of the United States intelligence community and other national-security related organizations, including Combatant Commands, and federal departments. The wikis are not open to the public.
For more on this, consider this article about how the intelligence community is using social media to get better at information sharing.