Calais is a free API from Thomson Reuters that uses natural language processing to automatically tag people, places, events and other entities in text content. This makes content more interoperable and searchable. Several startups and websites like The Mail & Guardian are using Calais to better organize content, enhance search and create more personalized experiences for users. Developers can get started with Calais through its open API or pre-built applications for Drupal, WordPress and Yahoo SearchMonkey.