GeoClass for PHP provides classes to handle georeferenced data. It can search databases which contain latitude/longitude for a location to find locations within a surrounding area. Conversion between data formats and distance-calculations are provided.
Geoblock is a program for 3D modeling, database management and visualization of geoscience datasets. It is designed for mineral deposit exploration, ore reserve estimation, mine planning and simulation of processes in mine sites.
GeoTools is an open source java toolkit for developing interactive geographical maps. The emphasis is on client side mapping applets which require little or no server side support. The main file format for the moment is the ESRI shapefile
By the way, the site is done in Drupal, a highly sensible, capable and flexible CMS, or content management system (an initialism that uses two of my three least favorite words). My only complaint about it is its twist on the meaning of "blog." As I understand it (and I may be wrong, "blog" is the name Drupal gives to any one writer's collection of posts. So mine is called "Doc Searls's Blog." Given the name we use over here, that can be confuzzing.