GRASS - Geographic Resources Analysis Support System is a general GIS supporting processing, analysis and display of raster, vector, site and imagery data, geospatial modeling and visualization.

1982-1995: developed at US Army Construction Engineering Research Laboratory, Champaign, Illinois, USA
1999: released under GPL
2001-present: development coordinated at Istituto Trentino di Cultura, Trento, Italy and CVS support by Free GIS project, Intevation Gmbh, Germany.

GRASS is an Open source / Free sofware released under the GNU General Public Licence - it is therefore free with protection of the authors' rights. With its 1.5 million lines of C code it belongs to the Top10 Open source projects.

Overview of GRASS versions currently available:
 

• GRASS5.1 - new version, currently under development
• CVS GRASS - continuously updated developers version
• GRASS5.0.* - current stable release
• GRASS4.3 - last non-floating point release
• GRASS4.1 - last official CERL release in 1991

GRASS development structure

Additional reading

History of GRASS

Freedom in geoinformation science and software development: A GRASS GIS contribution (Helena Mitasova and Markus Neteler)