GRASS GIS 6.4.1-2 - Geospatial data management, visualization and analysis.. (Free): 
GRASS GIS, commonly referred to as GRASS (Geographic Resources Analysis Support System), is a Geographic Information System (GIS) used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization. GRASS is currently used in academic and commercial settings around the world, as well as by many governmental agencies and environmental consulting companies.
- Mac OS X 10.6 or later
- Apple's X11
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