CKAN is the Comprehensive Knowledge Archive Network, a registry of open knowledge packages and projects (and a few closed ones). CKAN is the place to search for open knowledge resources as well as register your own – be that a set of Shakespeare's works, a global population density database, the voting records of MPs, or 30 years of US patents.
Those familiar with freshmeat or CPAN can think of CKAN as providing an analogous service for open knowledge.
CKAN is developed and maintained by the Open Knowledge Foundation. Both the CKAN code and data are open: free for anyone to use and reuse. To find out more check out the the CKAN project at knowledgeforge.net