The 6.4 version of GRASS GIS for Mac is available as a free download on our software library. The most recent setup file that can be downloaded is 87.7 MB in size. The application is included in Education Tools. Our built-in antivirus scanned this Mac download and rated it as virus free.
From the developer:
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.
You may want to check out more Mac applications, such as GRASS-, spatialite-gis or Quantum GIS, which might be related to GRASS GIS.