[oceanician]

Going to be harder for people to clone that than Reader :/

[seanalex]

Out of curiosity, why do you say that? I would expect it's as simple as creating a polling/request call to the phone's GPS coordinates. The data can be stored on an application's server and then displayed onto any mapping choice for that person's "group".

I haven't dabbled much in mobile development, so I really couldn't say how hard it overall would be.

[mzahir]

Reader is actually harder since it provided RSS feeds for websites that didn't support RSS (using the in-house indexed data)