CKAN is the Comprehensive Knowledge Archive Network, a listing of open knowledge packages. Those familiar with freshmeat or CPAN can think of CKAN as providing an analogous service for open knowledge. CKAN is the place to search for knowledge packages as well as register your own.
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