ConceptNet
ConceptNet aims to give computers access to common-sense knowledge, the kind of information that ordinary people know but usually leave unstated.
The new version of ConceptNet, ConceptNet 5, is now maintained in a separate repository:
http://github.com/commonsense/conceptnet5/
See http://conceptnet5.media.mit.edu for more information.
If you're interested in ConceptNet, please join the conceptnet-users Google group: http://groups.google.com/group/conceptnet-users?hl=en