Yikes. I've been working on an iOS based competitor for the past three months. My concept is a bit different. I'm using photo data from public sharing sites and clustering geotag locations to determine scenic or popular points of interest. Users can then create custom walking tours to one or more of these locations.

I've only got a few days left of development, so I'll probably get it out before Niantic/Google's iOS launch. The good news is that Field Trip seems fairly well received so far so there's a demand for this type of thing.