The TownMe API, at GeoAPI.com, has now been fully incorporated into Twitter's services. Before the acquisition, it included both read and write geo-related services. The read side had a reverse geocoder which helped translate coordinates (AKA lat/longs) into human readable elements or associations. For instance, give the API "37.78093,-122.409415" and it returned information about the census tract, neighborhood, city, MSA, and state that contains these coordinates.
The POI Finder took a lat long and gave a set of points of interests including businesses close to that point. This meant anyone could build services that allowed users to broadcast location or otherwise interact with their "real location".
The write components of the API included: