The Geographic Resources Analysis Support System (or GRASS GIS) is an open source, Geographic Information System (GIS) package. GRASS has over 200 tools and programs, which can be used to manipulate, display, and import/export many raster, vector, and site data formats. It is released under the GNU General Public License.
GRASS is used for data management, image processing, graphic production, spatial modelling, and visualization of GIS data. It is run through a Graphic User Interface (GUI) or from the command line.
A Brief History of GRASS
In 1982, the U.S. Army - Construction Engineering Research Laboratory (USA-CERL) released the first version of GRASS. Originally, the military used it as a land management and environmental planning tool. But over time, GRASS evolved into a powerful tool used in a wide range of scientific research fields.
Currently, GRASS 6.2 (stable release) is supported by the GRASS Development team lead by Markus Neteler at ITC-irst, Trento, Italy. The GRASS-Wiki provides a collaborative Help system for users and developers.