CloudMark (http://www.cloudmark.com) is a way of combatting email spam by sharing individual users' feedback on specific emails - those marked as 'spam' by enough users are fed back to all users, helping software such as SpamAssassin to classify such spams correctly.
Relevance to TWiki is as a model for fighting WikiSpam and its close relative, BlogSpam.
-- Contributors:RichardDonkin