Hi friends!
As some of you know, I recently started working with De Novo Group, a non-profit composed principally of a bunch of CS researchers out of UC Berkeley.
One of our core projects is called Rangzen. It's a mobile messaging app that works over Bluetooth and Wi-Fi Direct to forward messages anonymously over time. It uses mutual contacts to prioritize messages based on trust (this is done using crypto to secure the actual identifying information of mutual contacts).
It's early beta right now and very experimental. The current version of the app shows you where you've been, and drops pins when it discovers others using the app nearby. The GPS tracking would be disabled in the final version of the app - for now, we're using it to study how mobility patterns affect the exchange of information within the mobile mesh network it creates.