Cloak uses public location data from other social networks, Foursquare and Instagram, to determine the locations of others you know. Users can choose to receive an alert when certain people are believed to be nearby. It is the latest in the recent trend of "anti-social", or secretive, apps.
I am here by the will of the people and I won't leave until I get my raincoat back. - a slogan of the anarchists in Richard Kadrey's "Metrophage"