Encounter Bubble: another Location Based System that seems interesting. It is based on relative awareness.

The system is built around the concept of “encounters." Each encounter consists of a pair of devices, a start time (when one of the devices detects another), and an end time (when the devices pass out of range of one another). An encounter can be registered when two users (represented by two mobile devices) come within range of one another, or it can be registered between a user (represented by a mobile device) and a place (represented by a stationary device such as a wireless Internet access point). Mobster currently works with wi-fi (wireless internet) devices, but it can be extended to work with Bluetooth devices, cellular telephones and with devices that will use future wireless protocols as well.

The Mobster client application lives on a user’s mobile device or laptop computer and it registers encounters. The client sends its encounter records to the centralized Mobster server application which maintains a database of users, places, and encounters. On the server, each place can be “tagged” by users with a text place name. Users are recognized by unique identification numbers associated with their devices. For instance, if Mobster runs on my laptop, the Media Access Control (MAC) address of my wi-fi adapter card would be recognized and recorded by the Mobster system, and by registering with Mobster via the Web I can associate my name and profile with that MAC address. Privacy mechanisms will enable users to mask some or all of the information they submit to the system from others.