MapServer is a system for developing web-based GIS applications. 
The basic system consists of a CGI program that can be configured to 
respond to a variety of spatial requests like making maps, scalebars, 
and point, area and feature queries. Virtually all aspects of an 
application, from web interface to map appearance can be developed 
without any programming. For the more ambitious user, MapServer 
applications can be enhanced using Java, JavaScript or many other web 
technologies.

WWW: http://mapserver.gis.umn.edu/