Face2face

face2face is a proprietary proximity-based mobile application developed by Proximate Global Inc. that allows users to identify when members of their social networks are nearby, within walking distance, without sacrificing privacy.
face2face was launched in July 2010 for smartphones including the iPhone, BlackBerry, Android, and many J2ME-compatible devices. face2face does not reveal precise location coordinates, although its technology gathers that data.
In its first month (July 2010), face2face had 10,000+ app downloads. Those users are then connected to 3.5 million friends of friends.
Overview.
face2face compiles existing online social and business networks including Facebook, LinkedIn, MySpace, and Twitter and enables users to see when members of these networks are in close proximity, although it does not reveal users' exact locations, protecting their privacy.
face2face allows users to choose with which members of their social networks they share location information; people not in one of their networks cannot see the information. It works on BlackBerry, iPhone, Android, and many J2ME-compatible devices. face2face populates content based on users' news feed, statuses, and proximity. Users can also update their own statuses and share news across all of their social networks. 
The last version of face2face's user experience and interface was designed by a communication designer named Vakas Siddiqui.
Awards.
face2face earned Mashable's "Spark of Genius" award in July 2010.
Privacy and security.
Responding to growing concerns about location-based apps revealing too much information about a user's whereabouts, face2face incorporates "reciprocal sharing functionality" so that only users who make themselves known to each other share location data.