We used Open Source software as much as possible while building these pages. Most dynamic pages are built with PHP, and the web mapping pages use PHP MapScript. We use PostgreSQL with the PostGIS extension for our spatially-enabled data because it works wonderfully with MapServer. Although most of our non-spatial data are in PostgreSQL databases, we do use MySQL for some things.
In addition, we also use some of the GDAL utilities and some custom Python and C code that use the GDAL and OGR libraries for some of the data processing that happens dynamically. We also use some code written in IDL with the ENVI libraries for some of this processing.
Open Source Web serversApache HTTP Server Project - web server
Open Source Database serversPostgreSQL - database server
Free or Open Source programming/scripting languages and librariesPHP
Free or Open Source Geospatial SoftwareMapServer - tool for building geospatial web applications
Commercial SoftwareIDL - Language great for processing raster data